A few things I missed:
I angered the bratty Rapax Prince for the second time, hanging out with his Concubines in the Upper Rapax Castle (the first time I angered him was in the Rapax Away Camp, same thing, hanging out with his Concubines, where he teleported away, and his Concubines attacked me). This time, however, he ordered his Concubines to attack me, and teleported away again, but the Concubines never attacked me, because I am Rapax Templar. They did, however, stand around, and made it hard for me to get to their chest (I had to intensely squeeze through two Concubines to access the chest.).
The Rapax Queen, strangely, has a portal to the Arnika Temple in her room. I wonder why? It's either a planned Rapax invasion of Arnika, or because the Rapax Queen hates her life, and wants to escape (possibly to shack up with Antone)?. Nobody knows, as this is part of an unfinished quest, just like how using the slips on the strange machine causes my faction rating to decrease with an unknown faction, the Rapax Assassins.
Also, I got the Cat O' Nine Tails. Its damage is slightly higher than the Vampire Chain, by 2-3 points (I checked), but the Vampire Chain get a bonus to the Mace and Flail skill, and drains stamina. The Vampire Chain wins because it's "cooler", basically. Not that any of this matters, it's just a formality. The only remaining area is Ascension Peak, where enemies will scale to my level, and I will wind up with level 35-40 enemies, sometimes even a level 50 Armegazer. The Priest's melee capacity will not be a factor.

I checked, and re-checked later, all 3 levels of the Rapax Castle: The Rapax Castle Main Level, The Rapax Castle Cellar, and The Rapax Castle Upper Level. This ensures that I first do everything, in sometimes strange order, then, coming back later, in logical order, makes sure that I did everything. The Rapax Castle is entirely cleared out, all 3 levels.

My mission tonight was to deactivate the Dark Savant's bomb, having gone through the Rapax King's room to access the portal.
I first had an easy battle with a total of 7 enemies, 3 Savant Berserkers and 4 Savant Gunners. No problem. I saved after that.
Then, weirdness happened. Sometimes, enemies from the lower level, who you can't even see, attacked me (some retreated). How annoying. I kept reloading, until the lower level enemies walked away, then circled around to check the area.
I disarmed the bomb by playing around. Luckily, there is no penalty for failure, and I managed to disarm the bomb before the wandering lower level enemies could harass me again.
After getting the 500K experience for doing so, I saved, and retreated, and let the lower level enemies wander away again. I checked the upper area again with Detect Secrets active, and found nothing.
After the lower level enemies wandered away, and it was safe, I took the elevator down to the lower level, and saved.
I then had a battle with 15 total enemies, 14 of which were unimportant (a mix of Savant Berserkers, Savant Gunners, and Savant Destroyers). I destroyed those other 14 easily with the hit-all, mass damage spells (Falling Stars, Earthquake, Mind Flay, and Nuclear Blast).
This leaves a unique enemy, the Savant Behemoth, an upgraded version of the Savant Minion that you sometimes see in Arnika. This guy is tough! He is very resistant to every magical element, and shrugged off most of the attacks that killed all the other machines (even at level 20!).
He took little damage from the "hit all enemies" spells, so I was forced to focus. I used the high-damage, single-target spells against him (Boiling Blood, Crush, Might to Magic) repeatedly, for several rounds. He eventually died, due to my party's superior level, and Powercast, however, my mana was severely depleted.
Not by accident, I did this at night, after 10pm (22:00 hours military time), when only weak thieves spawn, so it didn't matter that my mana was depleted when I portaled back to Arnika from the inner Savant Tower.
I had a couple of battles with puny Higardi Raiders (I could kill them with a flick of my pinkie).
Interestingly, out of the 10 residents of Arnika (Myles, Tramain, Vi Domina, He'Li, Llorac, Lord Braffit, Antone Rapax, Screg, Urq, and Anna La'Am), 9 of them had no response to "bomb deactivated". I just saved the whole town, and possibly the entire planet, from oblivion, and not even a word of thanks? What an ungrateful town.
The only one who cared was Lord Braffit, who said something like "Thank you for telling me that", and gave me experience points.

Addressing your concerns (I believe that I have enough rep points to do this, does that even matter anymore)?
The Mage can wear the Canezou Helm, which grants Vitality +10, but this is so late in the game that it probably doesn't matter, when you have to face enemies on Ascension Peak who use magic against you.
The Mage was the first in my party, however, to get 100 resist all, due to her +5 to all resistance profession bonus. All you have to do, is have a power level 7 Magic Screen buff, and unlock and max Iron Will (easy to train on the Lower Monastary trapped coffin that casts Noxious Fumes at the party). The other casters need the Cloak of Many Colors for that. This is assuming that you don't mind grinding your realm skills to 100. Otherwise, Cloak of Many Colors.
If you're going to make a Psionic, I would suggest going with a Human. I managed to get his Intelligence, Piety, Speed, and Senses maxed by level 27 (perfect synergy), and the other stats were at least 45.
How resistant are you to grinding? I mean both skill grinding, and item grinding?
I'm trying to help the W8 community by pointing out that there are two set Rapax Corpses right when you enter the Rapax Rift, near Rafe's cell. You can grind Staves of Doom from them with a 10% drop chance, or, failing that, at least get the Bonebasher Staff. I didn't even know that you could farm them for two more Staves of Doom, until this playthrough, when my curiousity got the best of me, by messing around with Flamestryke's website.
If in doubt about racial choices, go with Human. They get a minimum of 45 to all attributes, and the highest total stat sum. Attributes are something you can never get back, skills you can always grind, and resistance can always be shored up with Magic Screen, Element Shield, and Soul Shield.
Bottom line: MDPs like mine are very powerful. I cleared the Rapax Castle Main Level in 4 easy battles, something everybody else would have struggled with.

I've actually never obtained this particular item, and by the time it's accessible, HP is high enough that I don't need the bonus, and at this point I would have multiple characters with Resurrection. (Not counting the second Bishop, unless I do Rapax really early, my planned party would have 3 characters with this spell, which would later go up to 4.)

On the other hand, the extra Vitality does provide more room for healing spells to work.

Thing is, you need 100 base Piery to get Iron Will, and I feel that's too much of a cost, especially on a character who doesn't get status removal spells. I'm not planning on getting that skill at all, but if I were, it would have to be on someone who can cast Priest spells. (Although getting it on the Alchemist might be reasonable, since the Alchemist can cure all disabling conditions except the ones the Psionic is immune to, well and afflicted unconsciousness (unless I use Smelling Salts).)

Also, for many races it may be easier to get Iron Will on a Bishop than on a Mage. (I haven't investigated this because I'm not interested enough in this particular expert skill, and certainly not on a Mage, as I mentioned.)

I don't expect to see level 27.

Humans don't get Power Cast as quickly as Mooks do, at least with this class. The one drawback is low Piety, but Piety is less important when you know more spells of a realm due to the way the formula works, and Psionics can learn all but 2 Mental Magic spells. (Not to mention that Mental Magic is the primary realm for them.)

Humans, from what I can tell, work best for more balanced builds, or those that require lots of stats for their class and are focusing on some stat the class doesn't get. (For example, a Human can be good for the battle Bishop build, getting Power Strike at level 17 while still getting Power Cast as 12 and not having terrible Speed.)

First, I don't like the term "grinding".

Secondly, I'm OK with it as long as I don't have to constantly reload. Hence, I'm generally OK with raising skills, but not OK with farming items. (I'm actually considering using Cosmic Forge to add the Bullwhip to Burz's and/or Antone's inventories just so that there's a reliable early source for that weapon. This is in addition to adding the Mind Stab/Holy Water books to shops, and making Bela sell Rings of Power (I want to see how that feels).)



But your party is massively overleveled.

Try doing this with a party in the teens that has not been to the Sea Caves, as that would provide a more realistic idea of how well the party behaves.

The HP progression for casters is Priest>Alchemist>Bishop>Psionic>Mage. However, the Bishop levels slower than the specialist casters, and will probably be a few levels behind, so you would think that the Psionic's HPs would be similar to the Bishop's HPs. The Mage will always be behind in HPs. However, in my party, the Psionic is 20 HPs above the Mage, with the same level and Vitality. Giving the Mage the Canezou Helm increased her Vitality by 10, adding 8 HPs. Now, the difference in HPs between the Psionic and Mage is only 12.
Having nobody to cast the Wizardry/Mage spellbook means that you get no Missile Shield, Enchanted Blade, or X-Ray (unless you have a Gadgeteer, but getting that gadget requires getting into the Mook HQs). Without a Mage or Samurai, your only means of those spells is the Bishop, who will have to have a primary focus on Wizardry.
Without a Bard, Gadgeteer, Rogue, or Ninja, who will handle Locks and Traps? Who will tank, and handle melee fighting? The Valkyrie will be doing all the heavy lifting, as a Battle Bishop will be squishy, as well as a Priest, at least early on. I'm assuming you will recruit Vi Domina, and RFS-81? I don't like RPCs, but you might.
I don't like carrying around consumables, as they add a lot of weight, causing encumbrance. Also, I don't use charges on items (except Mana Stones; Their sole purpose is to restore SPs). Both of these require frequent returns to a vendor (the former to restock consumables, sometimes requiring camping, and the latter to sell and buy back, to recharge items).
I like being all-powerful, being able to slay all opposition with powerful magic, enhanced by Powercast, something you don't get from consumables and item charges. I have a godly MDP, being worked on for almost 2 years, everybody being decent at melee combat, ranged combat, and magic combat. I'm Lord Palpatine in the flesh, mwahahaha!
My Alchemist, Psionic, and Mage have a poor 1-handed weapon selection: Daggers, Wands, and Short Staves. The Psionic and Mage can't even use Shields, and the Alchemist with a Shield and 1-handed weapon would suck. Therefore, I put all 3 in the protected center formation, and gave them Staves of Doom to attack from extended range. The Bard, Gadgeteer, and Priest are holding the front, left, and right flanks, with their 2 *Light Swords*/1 Vampire Chain and 3 *Light Shields*. Granted, ranged combat is entirely unnesessary if you have good melee and magic capability, so I don't need to carry around all that heavy ammo, keeping everyone in white enbumbrance, and maximizing my initiative, and number of swings and attacks per round. Look at a Bloodlusty Bard or Gadgeteer as an example.
You don't do the Rapax Templar initiation with Al-Sedexus? What do you do then, kill her right away after killing El-Dorado? If you talk to her the first time, she will instruct you to see the Rapax Templars in the Rapax Castle, and then disappear. I'm assuming that you have to initiate combat with her while she is friendly?
Or, you talk to her, then leave the Rapax Rift, and return, and she will be back in her chamber, this time as neutral, and if talk to her a second time, she will attack you, and you can kill her (I don't think that this happens, as she is waiting for you in the Rapax Castle).
Or, can you kill her after she appears after pouring Dark Nectar on her throne?
Or, you could ignore her entirely, and have to fight constant waves of Rapax in their castle, just to explore it.
Perhaps you are right about Piety. The increase in SPs from adding to it is small compared to the increase from knowing more spells in a realm. Perhaps the developers should have made Piety count more towards SPs. I believe that Piety is worthless for non-casters, mediocre for hybrids, and unnecessary for Bishops, who know so many spells that they have excellent SPs. The specialist casters benefit the most from this attribute, who only know one spellbook.
Rings of Power is an interesting idea. My casters have Robes of Rejuvenation, providing +1 HP, +2 Stamina, and +1 SP regeneration. Extra Rings of Power would give the casters an additional +2 SP regeneration, as well as charges of Restore Magic.
This would make up for the fact that the Fighter, Lord, Valkyrie, Ranger, and Samurai can all equip the Infinity Helm. It gives +2 HP, +5 Stamina, and +5 SP regeneration. This would make casters broken, the game developers probably thought. The hybrids are stunted in their relative caster level (-4 compared to a full caster), so the developers probably thought that this would help "even out" the hybrid casters, who probably have low Piety, and hence low SPs (the Ninja and Monk get Stealth, so they don't need that heavy protection).
Lastly, what do you mean that I'm "massively overlevelled"? Not counting Ascension Peak, most areas in the game spawn monsters that max out around level 20-25. The exception to this is the Mountain Wilderness, where you can get Crag Sprites and Mountain Sprites around levels 25-30 (fortunately, these battles can be avoided with care, as they start out neutral). The elephant in the room is level 34 Molten Scorchers (very high experience points). How are you going to have a party in their 20s in that area? Obviously, the mid 30s is a level that you can dominate every area in the game before Ascension Peak (where level scaling resumes).

Only a couple levels difference, at most, and that's assuming equal XP and that everybody levels up at the same time. (One approach would be to hold the levels of faster leveling characters until the slower levelers catch up.)

Also, that Canezou Helm could have been given to the Psionic instead, widening the HP gap. (Although, of course, the Psionic might want the Cap of Wiles instead.)

I've thought about this. Thing is:
* A Bishop can learn Missile Shield and Enchanted Blade at level 3 without practice.
* There's plenty of practice opportunities before X-Ray has to be learned, and in practice a Bishop is likely to not need the full 45 points because of spells like Identify Item.
* High Intelligence means that Wizardry will grow faster.
* The primary focus on Wizardry is only important up to 4th level spells, as the higher level Mage spells are less critical. Dehydrate, Firestorm, and (with the Mindblast Rod) Nuclear Blast can be covered with items if needed (they aren't). Blizzard I don't like because of the Blind effect, and at high levels Tsunami replaces it, which being easier to cast at decent damage amounts (less Water skill required, when comparing damage rather than power level). In the teens, I'd rather have Ego Whip and Psionic Blast over any Mage-exclusive spell at level 4+ that isn't Iceball.
* Also, don't forget that this party would have *2* Bishops; only one needs to cover these spells.

Not planning on recruiting RPCs.

The Priest and melee Bishop will be using Mace & Shield, so AC shouldn't be that terrible. Also, Guardian Angel can make up for lower HP, and there are 3 people who can learn that spell. (Bless also helps.)

Also, many battles will be over before the enemies can do threatening amounts of damage. (I saw someone kill Gregor with a 6 mage spell without Gregor being able to act.)

For Locks & Traps, there are options:
* Knock Knock, particularly when multiple characters can use it. (3 can use it in this version of the party.)
* Posseur's Cap, later combined with Thieves' Buckler, allows for raising the last tumbler or two.
* Forcing the lock with whoever has the most Strength is also an option.
* For traps, save before first inspecting, then use Knock Knock to open. If the trap is a problem trap (like Philosopher's Bane or Heatwave) and it gets tripped, reload. If the trap isn't a problem trap, can just heal the damage and conditions received. (In the case of Anti-Magic, some rest and re-casting spells will fix it.)

I'm trying to get myself to use consumables and charged items more often. Hence why I may build the Alchemist for bomb usage and hopefully get the Psionic using Artifacts.

Case in point: Burz sells an item that casts Energy Blast (5). Get a few of them, use them against Gregor, and if they don't fizzle/backfire, the battle should be significantly easier. I've heard that a Stink Bomb can also work here. (There's also Blinding Flash, and Alchemists don't get that many good low level spells, anyway.)

If I'm able to get Rings of Power to be buyable, they can also be used to cast Restore Magic, albeit at a lower power level.

(Also, worth noting that, in the CRPG I'm making, every item will have limited uses, though some characters will have the option of using MP instead for certain types of items. This means that the only way to escape the use of item charges will be to spend MP, and I plan on balancing things so that it can easily run out if you want to use your strongest weapons all the time.)

Or, I could just stop playing before I have to do that quest to progress, which is what I've done.

Or, avoid having multiple artifacts at the same time, except when doing the Umpani-T'Rang Alliance quest.

Here we go: *cue the music* Europe: The Final Countdown! Time to explore Ascension Peak!
Every area except for Ascension Peak has been fully explored, except for one area in Lower Marten's Bluff, where two T'Rang threaten you (Project Mindblast). I have no interest in pi$$ing off the T'Rang, or having them get in the way in the corridors, and the Mindblast Rod has a severe penalty to initiative.
I have angered the Rapax Prince twice, both in the Rapax Away Camp, and in the Rapax Castle. Twice, he has teleported away. I wonder where he could be? Surely, not waiting for me in the last area of the game, Ascension Peak?
I explored Ascension Peak, from the portal to/from the Rapax Main Castle level, past the landslide, up to the fountain pointing three ways. I would say that I am done here, having 3 ways to go, and locks in all 3 directions. I grabbed all treasures along the way, and filled out the map.
By the way, I was wrong about ammo. I am man enough to admit that. In one battle against Gazers, I managed to kill all but one in round 1, then the last Gazer cast Eye for an Eye against itself, as well as Body of Stone. I had to use my characters' ammo against it, lest I suffer backfire from casting magic against it. However, thankfully, this is rare. I did manage to return to Ferro, and buy a lot more ammo this time around, resting and saving.
I would say that I am 25% of the way through Ascension Peak, counting the legs from the Mountain Wilderness, and the Rapax Castle Main Level, up to the central fountain.

I'm pretty sure that applies only when you are using it as a weapon, which is not how I would typically use it. (Bishop and Psionic don't get the weapon skill and therefore aren't effective with it, while Monk has better options, not to mention that the Stun Rod is about as good if you don't count the as item effect). If I use the Mindblast Rod, it would be as an item to cast Nuclear Blast (3), not as a weapon to swing in melee.

By the way, there's a way of manufacturing real combat anywhere, including the cleared out Rapax Courtyard (and, I believe, the Cosmic Circle pre-final battle). It works as follows:
* First, start fake combat. Have someone cast Summon Elemental, then swtich to continuous combat.
* While the summon animation is playing, go to someone else's spell book. Have that character cast a single target damage spell, and target the summoned elemental.
* Once the spell goes off, the elemental will turn hostile, and you will now be in real combat as a result.

Note that this doesn't give you any experience points.

RAnged attacks are affected by Body of Stone as much as melee attacks.

Eye for an Eye can only reflect a limited number of spells. Therefore, on strategy is to spam weak spells (like Energy Blast (1)) on it, so that the backfires don't hurt you significantly, but it still uses up the Eye for an Eye. Then, once that's down, you can blast the enemy with your spells, as long as it doesn't recast the spell.

Alternatively, get your resistances up high against your own spells.

My current party doesn't use ammo. My planned next party will have a couple characters (Alchemist and Psionic) using ammo, at least at first (Alchemist may switch to Staff of Doom at some point, but will still be able to throw bombs).

The MindBlast Rod is only available to Monks, Bishops, and Psionics (anybody with the Psionic spellbook). However, my Psionic has a Staff of Doom, arguably better in melee (not that this matters on Ascension Peak; It's all about magic and ranged damage.)
Fighting on Ascension Peak is actually a great way of getting experience points; I'm more than halfway to the next level.

Thing is:
* The Staff of Doom is definitely better if you're using it as a weapon, particularly for Psionic or Bishop.
* As an item, however, there's a trade-off. When fighting higher level enemies and/or on expert difficulty, Death Cloud doesn't work that well. However, Nuclear Blast still does work well. At lower levels, the damage from Nuclear Blast (3) is significant (more than Fireball (7), for example, at least pre-Power Cast). Even at higher levels, Nuclear Blast can be handy when the enemies have used Soul Shield and the enemies aren't lined up for Psionic Fire; the only reasonable Psionic spell alternative at this point would be Prismic Chaos.
* Also, the Mindblast Rod has far more charges and is less of a pain to recharge. Furthermore, it's less likely to fizzle or backfire (and with decent HP, the backfire won't kill anyone if it does happen, which is more than can be said for the Staff of Doom).
* Don't forget that it's easy to switch between the Mindblast Rod and a sling (particularly handy if this Psionic has Eagle Eye from maxing Senses), whereas it's not so easy with the Staff of Doom.
* On the other hand the Mindblast Rod requires some trickery to get that some players aren't comfortable with. It also can't be used (as an item) in the Sea Caves, and is less effective against Scorchers.

(It's a shame these weapons are both two-handed; it would be nice if one could dual-wield with a Winterwand to have its Iceball spell, which could be handy in Rapax territories, available.)

In youtube videos, I've seen high level solos get multiple levels on Ascension Peak, and that's without farming extra encounters.

Made a mod to add a few items to stores for my next playthrough:
* Burz and Antone: Bullwhip. This item does have a good chance of appearing on its own, bot otherwise you can't buy it until Kunar/Sadok, and it's the sort of item that's fundamental to my character builds (at least until stronger alternatives appear late game).
* Anna: Book of Mind Stab. (This item exists in the game data, but isn't actually found anywhere in-game. All it does is teach a certain 1st level spell to the user, anyway.)
* Braffit: Book of Holy Water. (This item is normally a random drop from one specific Savant Orb (that doesn't respawn), and from Braffit (who I would rather not kill). Again, all it does is teach a specific level 2 spell to the user.)
* Bela: Ring of Power. It's a powerful item (+2 SP regen, +2 AC, 4 charges of Restore Magic (3)), but it's normally nearly impossible to get, as Bela, who in theory drops this item when slain, can't be targeted. (Trying to "Attack" him has him respond as though attacked, but combat doesn't start.)

On the way, my level 19 party encountered 3 level 25 Bitter Wings. Their breath cuases poison that was hitting for sometimes as much as 40+ damage at the end of each round, so I ended up using multiple Heal Alls to be sure that at least one would go off even on rounds I had to move. Their level was too high for spells; the Jackhammer did maybe all of 2 damage.

I have a Mage and Bard to cast Nuclear Blast (the Mage at power level 6, as I don't like the small chance of failure, and the Bard at whatever power level the RNG casts it at). There is no need in my party for an item charge of Nuclear Blast power level 3.
I believe that Element Shield helps protect against getting poisoned in the first place, and poison damage in general. Does poison fall under the air realm? Cure Poison is an air realm spell.

The situation to consider is when enemies cast Soul Shield. What does your Psionic do in that situation if cone spells aren't workable? Prismic Chaos?

Also, for the party I'm planning, I'm not going to reach a high enough level to cast Nuclear Blast for a while, and even then, only my Bishops will be able to learn it (and probably won't learn it until later, as I consider it lower prioirity than the other nukes).

Element Shield can only prevent getting poisoned if I'm not already poisoned. Worth noting that the caster Bishop might have had a chance of doing some damage with a spell, while the Bard and Gadgeteer weren't doing anything else (and at this point, stamina cast Heal All will work reliably). Everyone else was busy using melee attacks. I'm not aware of any mechanic that would allow Element Shield to mitigate poison damage. Guardian Angel can block poison damage, but it's only single target, and so are Cure Poison and Restoration, the two spells capable of removing the status.

In Wizardry 6 and 7, Poison and Deadly Poison are Air realm. (Too bad these spells aren't in Wizardry 8; Air is the only realm left without any single target offensive spells, an the only spells that can poison are Toxic Cloud and Prismic Ray/Chaos.)

The Knowledge Temple! This is the shortest path, of the 3. I fought Amit and Pee-Wee (I don't take kindly to threats; Similarly, I refused all Rattkin "protection"). Pee-Wee was almost immune to magic, and I had to use ammo against him (this time, the on-weapon maluses took effect). This cleared the way. After a bunch of nonsense, I had a caster (level 36) waiting for me, near the Knowledge Temple. I guess I'm not so "overlevelled" after all?
The Destinae Dominus is the first artifact you will want to dispose of, as it frees another slot in the character's personal inventory. For example, my Alchemist had the Helm of Serenity, and Destinae Dominus in his personal inventory slot. Since depositing it, he now wears a Brilliant Helm, and has personal inventory slots for 8 Mana Stones.
I have to be 50% done with Ascension Peak, having cleared out the entry, plus the "Knowledge" route.

Because the Helm of Serenity gives mental resist, I would consider leaving it equipped on someone, or at least equip it for any fixed battles that have insanity/turncoat casting enemies. Generally, I'd give it either to someone who can cast Sane Mind (but not a Psionic, since they're immune to mental statuses) or to someone with a deadly physical attack (the sort of character who you do not want to go insane or turncoat). Or, you could take advantage of the fact that anyone can equip it. (All equippable quest items can be used by everyone.)

By the way, another thought: Daggers for an Alchemist? Specifically, the Canezou Dagger, while not that srong, is still stronge than any 1-handed wand that isn't fairy exclusive (and the ones that are stronger are only available as random drops).

Also, wondering which of these builds has more Artifacts in the mid-game: Int/Sen Psionic (starts with 0, but gets skill increases quickly), or Int/X Bishop (X != Sen), who starts with more, gets the 25% primary skill bonus, but doesn't get skill increases as often. In any case, Psionic needs Artifacts more than Bishop, in order to cover gaps in spells known (but one might also want Throwing & Sling, to allow use of Ice Bombs comfortably).