I remember reading somewhere that, apparently, you can still level up after reaching level 50.

Also, at the highest levels. apparently an integer overflow occurs with XP requirements which can cause Bishops and Ninjas to level up faster than other classes, so the very last level or so might go faster if you multi-class into such a class at the last moment.
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Let's be honest. My computer will probably die before reaching level 50 (or me, not to be morbid). It's a nice thought though, that I would have the patience for that, to constantly kill high level enemies.
I have in my fantasies that my Bard and Gadgeteer have Light Swords, and my Bard, Gadgeteer, and Priest have Light Shields.
At this point, class-changing the casters to Bishops would probably be a bad idea, as the 3 ignored spellbooks for each would start at level 1 spells. It would take forever to level at this point, as they would be treated as level 30 Bishops, with the heavy experience required to even open up level 2 spells.
I thought about making the Bard and Gadgeteer Fighters, but then I remembered that you actually have to BE a Gadgeteer to merge gadgets together, and I have only found a few gadgets. I believe that the Bard-turned-Fighter can still use instruments found, as they come fully formed, and I have 100 Music skill. But then I would lose the 25% Communication bonus (higher prices to buy at shops, lower prices when selling items). Also, no double camping bonus (hit points, stamina, and spell points recovering twice as fast).
What you described sounds like cheating, but that's something open to interpretation. Everybody has their own ethics code. I'm doing it the hard way, fighting normally, without bots, so it would take way too much time to get to level 50 honestly.
Edit: Does anybody know how the game would act if 6 attributes were maxed, and you could only put points in the 7th attribute? Would the game show mercy, and allow you to put 6 points into the last attribute at level up, or would you get screwed, and only get 3 points?
Similarly, if 5 attributes were maxed, you would be forced to put 3 points into the last 2 at level up, unable to even them out.
This is why I like having 3 attributes left to raise, as I have the freedom to even them out as I see fit.

The level at which the class change would give you faster leveling is, I believe, more like level 49. (It should be easy to calculate it; just look for the point where gaining another level would be expected to take more than 2^32 XP (about 4.3 billion) after class chanige.)

Thanks to the integer overflow, the XP required to level up from 49 to 50 would be significantly lower than what would be expected.

(Of course, you'd have to reach this level first, and with XP requirements growing exponentially without bound (until integer overflow occurs), that will take a long time.)
I generally don't consider glitches to be cheating. Some glitches could be exploited to make things significantly easier (like the identify glitch in the original version of Wizardry 1), but this particular one doesn't kick in until such a high level that it doesn't give the player a meaningful advantage.

(The game does have some negative glitches as well, like one that happens when you use "use last item" to use the last of the item, or when Remove Curse cast from the inventory backfires and the resulting hex causes the caster's SP to go negative, but both those glitches aren't useful, as they immediately crash the game. The only glitches that seem to actually be useful are things like clipping out of bounds or the save warping glitch that the speedrun uses, but all they let you do is go places you couldn't normally go or warp around.)

I believe that the level up factor is 2 up until level 11, which means it takes twice as much experience to go up a level as it did previously. Getting from level 1 to 10 is the same experience as getting from level 10 to 11.
After that, the factor becomes 1.2 (you told me this a long time ago.) So each level up takes 20% more experience than the last level up. Getting to level 30 was around 10 million experience for my casters, so getting to level 31 would be around 12 million exp.

What's interesting is what happens near the bottom of the table. Looking at an XP table online:

For pure caster:
48->49 takes 313,550,179 XP
49->50 should take 376,260,214.8 XP
49->50 actually takes 376,260,214 XP

For bishop:
48->49 takes 418,066,750
49->50 should take 501,680,100 XP
49->50 actually takes 72,183,370 XP, or 429,496,730 less than expected

2 ** 32 is 4,294,967,296

It appears that the game stores XP requirements to level up in tenths of points, given that the overflow happens around 430 million rather than 4.3 billion.

Worth noting that XP overflow also affects hybrids at this point.

Conclusion: To level up faster, change to a hybrid or bishop at level 49, and level 50 will be faster.

With all this said, it's not practical to actually reach this high of a level in the first place, so this bit of information isn't going to be useful to most players.

I'm not a fan of class-changing characters anyways, as I feel that, somehow, it's cheating the original class. For example, the Gadgeteer has job security of insuring that nobody ever uses her Omnigun or gadgets after a class change.
Changing a Bard to a Fighter is supposedly do-able, as I believe anybody can use her instruments, provided that they meet the Bard level requirements and Music skill. However, I would feel like I turned my back on the Bard class if I changed her to a Fighter. Knowing me, as a new Fighter, I would immediately load up on heavy Fighter equipment, immediately subjecting myself to heavy encumbrance, with the caster-heavy party unable to subsidize that heavy load.
I suppose that there is a reason to keep your class, the game penalizes you with the loss of your previous abilities for a reason. Besides, the Bard-turned-Fighter would lack in hit points, compared to what a Fighter of that level should be.
Edit: Also, a new Fighter with 100 Strength and 50 Vitality would struggle with all that heavy Fighter equipment, combined with all those instruments to carry around in her personal inventory.

I've found that, later in the game, heavy armor just isn't worth it (except the Infinity Helm, which I feel shouldn't have had more SP regen than anything pure casters can equip). Battles become easy enough that you don't need to optimize your AC, and the classes that can actually wear heavy armor tend to have enough HP that they don't need such armor. Also, healing is decently strong in this game, and infinite outside of battle once you have a level 11 Bard or Gadgeteer.

Also, many of the heavy instruments aren't that important. You really only need one of Lifesteal and Concussion, and the other heavy instruments either aren't worth the weight (Silent Lyre, of which there are 2 for some reason) or are not items you'll be obtaining (Lyre of Cakes, which does the same thing as the Dulcimer of Mending, but with there being 2 Dulcimers and 0 Lyres, the choice between the two is already made for you).

Keep in mind that encumbrance can weaken your offensive capabilites and harm your initiative, causing combat to take longer. At the point where combat is no longer a serious threat, winning the battle faster is more important than trying to avoid character deaths, not to mention that the enemies will get fewer opportunities to attack. (Even then, you can just heal whoever gets hurt; this becomes especially true if you have 2 characters that can cast Resurrection (or a Valkyrie who can cast Resurrection and cheat death), so that a single death is not going to force an item use or a reload.)


Gadgeteer gadget weight feels a bit more balanced, with the high level gadgets all being heavy, so the choice feels like it makes more sense there.

I forgot to mention all those special lightweight Bard items too. Namely, Ariel's Slippers, Oberon's Greaves, Caliban's Cuirass, Prospero's Cloak, Mercucio's Blade, and Ring of the Road. Also, Puck's Cap, if you count that as a Bard helm. With just the Ring of the Road and Caliban's Cuirass, I could have 125 Strength, combined with a bunch of lightweight armor that gives various resistance and attribute bonuses. This keeps the Bard relevant throughout the game: Her unparalleled Bard-only items, Communication skill bonus, and improved party camping. With a Light Sword or Fang, she could lay down the hurt in melee combat, as well. Both the Bard and Gadgeteer have to be due soon for the 3rd attack per round to open up (they are level 30, with maxed Dexterity and Speed). They already get up to 3 swings per attack if in white encumbrance (why is it random, with a seemingly equal chance for 1, 2, or 3 swings per attack?)

Level 31:
Priest: (Spellbook complete)
Alchemist: Dracon Breath
Psionic: (Spellbook complete)
Mage: Sonic Boom (Spellbook complete)
I'm at level 31, the minimum level for chests to spawn the best items in areas I haven't visited yet (those that have a level sensor).
The Bard and Gadgeteer got 100 skill in Close Combat. This maxes out their melee fighting. They now have 100 skill in: Close Combat, Sword, Shield, Powerstrike, and Reflextion skills. They are on the sidelines now.
The Bard and Gadgeteer get a significant penalty in the number of swings and attacks they get, compared to the Fighter and hybrids. The Gadgeteer maxing everything still doesn't give her the third attack per round. She will have to wait a few more levels for it.
The Bard hitting 100 Close Combat gives her the third attack per round, because she has special equipment (Oberon's Greaves for +10 Speed, and Mercucio's Blade for +15 Close Combat).
This puts the Priest on the frontline, protected by Guardian Angel and Body of Stone. He has maxed out his Close Combat skill. His Mace and Flail and Shield skills are at 99 and 96, respectively (due to the controlling attributes of Strength and Dexterity being average). He will max these soon.
Everybody has unlocked the Eagle Eye skill, and they are training it, along with Ranged Combat, Bow (Bard and Gadgeteer), and Throwing and Sling (all 4 casters).
I trained Iron Will at the coffin in the Lower Monastery. This is the only skill I "cheesed". Since Arnika has no magic using enemies, and the point of a MDP is to hit hard and fast, I could not think of a fair way to train this skill. Perhaps the plant enemies, but they sometimes run away, and don't always spray when you want them to. The best example of training this skill "fairly" would be letting a low level Sige from the Arnika Road or Arnika-Trynton Road hammer you with spells until she passes out. Or you could open the coffin repeatedly. Same result, either way.
The Mage, with maxed Iron Will and power level 7 Magic Screen, has 100 resistance to all realms. Her profession bonus of +5 to all resistances isn't quite so useless, after all. The other casters have 95 resistance to all realms, until they can get the Cloak of Many Colors, sold by Bela and Ferro. Element and Soul Shields will still have to be cast occasionally, to protect the Bard and Gadgeteer with no Iron Will.
All four casters have at least 77 Powercast, as that's their forte, casting spells.
Edit: I may have broken the Arnika day map, finally. At this point, the game tries to match monsters with my level, but due to being level 31, sometimes can't. I wind up with any Savant machines possible, from low level machines to high level Savant Minion, and everything in between. This is good for training up the Priest's Shield skill, which is hard to do. Just have a low level Savant machine attack him up front.

Level 32:
Priest: (Spellbook complete)
Alchemist: Sonic Boom (Spellbook complete)
Psionic: (Spellbook complete)
Mage: (Spellbook complete)
I have finally picked the last of the spells available, having completed every spellbook. The Mage finally has over 100 hit points.
The Priest managed to max both his Mace and Flail and Shield skills. The former was maxed in the first battle after level up. The latter took many battles, which I fought honestly. Getting to 98 skill is about the point where things get tough. I got to 99 Shield skill by fighting fairly, many battles, over what seems like an eternity. I got the Priest's Shield skill to 100 in one battle, having defended against low level machines for about 200 rounds, until they tired out.
This concludes melee training for the whole party. The Bard and Gadgeteer have 100 skill in: Close Combat, Sword, Shield, Powerstrike, and Reflextion. The Priest has 100 skill in: Close Combat, Mace and Flail, and Shield. The Alchemist has 100 skill in: Close Combat and Staff and Wand. The Psionic and Mage are too weak for melee combat, and the Staff of Doom is taken by the Alchemist.
Having concluded melee training, the Bard and Gadgeteer focused on archery. They both managed to get 100 Bow skill, after hiding behind the Priest's big muscles (100 Shield skill, protected by Guardian Angel and Body of Stone). Their Ranged Combat skills are at 98, and Eagle Eye skills are in the 90s.
The casters are too busy with training Powercast to worry about their ranged skills. I did get their Powercast skills to 89.
Four of the party members have evened out their remaining three attributes. The Bard has 55 Intelligence (+5 from Trynton well), 55 Piety, and 56 Vitality. The Priest, Psionic, and Mage have 55 Strength and Dexterity, and 56 Vitality.
This leaves two party members with uneven attributes. The Gadgeteer has 60 Intelligence (+5 from the Trynton well) and 53 Piety and Vitality. The Alchemist has 60 Dexterity (profession requirement) and 53 Strength and Vitality.
Edit: I misspoke. The casters DO get ranged combat training at shootouts, where there are Savant Minion and Savant Destroyers. That just isn't their focus.
Double Edit: Snake Speed skill is something that seems completely random. My Mage has been screwed, compared to the other casters. Her Snake Speed skill is only at 90, while other casters are at 92 and 93, despite the fact that every caster maxed Speed at level 16. The Bard and Gadgeteer have their Snake Speed skills in the 50s, trying to catch up to the casters. It just seems so random when Snake Speed increases.

Level 33:
(All magic spells learned)
It's getting very difficult to level now. The only areas that will present a threat to me now will be the Mountain Wilderness and Ascension Peak.
The Bard and Gadgeteer are "perfect". They have maxed:
Close Combat, Sword, Shield, Powerstrike, Reflextion
Ranged Combat, Bow, Eagle Eye
Music, Engineering
Note that Snakespeed is random, and they are in the 60s and 70s for that. Nothing I can do about that, except participate in combat, and hope it goes up. Just defending counts as an action, by the way.
The casters are tier 3, meaning that they will get the worst in terms of number of attacks and swings. I did manage to get their Powercast skills to at least 95. Also, their Ranged Combat, Throwing and Sling, and Eagle Eye skills are being worked on.
Edit: Ranged Combat skill was maxed first for all four casters, due to the controlling attributes of Senses and Intelligence being at 100. He'Li, Antone, and Anna have run out of Bullet and Spike Stones at this point, and I'm forced to portal back to Burz for Bullet Stones. I may have to rest for 24 hours just so vendors restock stones, so that I can max Throwing and Sling, and Eagle Eye for my casters. It gets ridiculous at some point, being an Autist trying to get perfect characters.

Level 34:
This is probably the last time that I grind. It's getting tedious. However, what's the point of unlocking expert skills, if you're not going to max them, right?
The whole time that I was in Arnika, no friendly green dots (friendly to the party) died on my watch. Vi Domina was escorted safely to He'Li's bar, Myles is still prowling around the fountain, Lord Braffit has his 3 Lay Brothers wandering around, and the two Higardi patrols of 4 (8 total) are still wandering around town.
The four specialist casters managed to max Ranged Combat, Throwing and Sling, and Eagle Eye skills. Basically, they had to buy and use every dart (Feather Dart, Poison Dart, Doom Dart) and stone (Bullet Stone, Spike Stone) available. This came from Burz, He'Li, Antone, Anna, and Fuzzfas (portals to both the first and last).
The Bard, Gadgeteer, and Rogue (if I had one) get 3 attacks per round now, both in melee and ranged combat. This is assuming white encumbrance, maxed Dexterity and Speed, maxed Close or Ranged Combat, and maxed weapon skill. This is quite a penalty, considering that the Fighter and hybrids get it much sooner, and the casters will never get it until level 50.
I am pretty much done with skill grinding. Here are the skills that I maxed (100 skill).
Melee: The Bard and Gadgeteer maxed Close Combat, Sword, and Shield (ready for Fang/Light Sword and Light Shield). The Priest maxed Close Combat, Mace and Flail, and Shield (ready for The Mauler or Diamond Eyes, and a Light Shield). The Alchemist maxed Close Combat and Staff and Wand (ready for the Staff of Doom, since he is the toughest among himself, the Psionic, and the Mage). The Psionic and Mage are too weak for melee combat (worst hit points, worst armor selection, no shields).
Ranged: The Bard and Gadgeteer maxed Ranged Combat and Bow (ready for the Tripleshot Crossbows that they already have, and good quarrels/bolts). The four casters maxed Ranged Combat and Throwing and Sling (ready for Wrist Rockets and good stones).
Magic: The Bard and Gadgeteer maxed Music and Engineering. No Powercast for them, as they get no benefit from it. The four specialist casters maxed their respective spellbooks to 125 (Divinity, Alchemy, Psionics, Wizardry). All six realms were maxed (Fire, Water, Air, Earth, Mental, Divine, with the exception of the Alchemist not using the Mental realm).
Special skills: Mythology is maxed for everybody, with so many battles. Artifacts is at the soft cap of 75 for most characters. Communication is at 78 for the Bard (97 with the 25% class bonus). Locks and Traps is at 77 for the Gadgeteer.
Expert skills: The Bard and Gadgeteer have maxed Powerstrike, Reflextion, and Eagle Eye skills. The casters have maxed Iron Will and Eagle Eye skills.
Snakespeed is something that eludes me, because it takes forever to increase. My casters maxed Speed, and unlocked Snakespeed, at level 16, and it's still stuck in the 90s. My Bard and Gadgeteer are stuck with it in the 70s and 80s, It's time to accept that it will never max, and that my initiative is high enough.
Powercast: The Bard and Gadgeteer do not benefit from this. The four casters (Priest, Alchemist, Psionic, Mage) are at 99 skill.
Edit: The attributes are evened out as well. The Bard and Gadgeteer have maxed Strength, Dexterity, Speed, and Senses. The four casters have maxed Intelligence, Piety, Speed, and Senses.
The Bard and Gadgeteer have the remaining 3 attributes (Intelligence, Piety, Vitality) at 59 and 60. The four casters have the remaining 3 attributes (Strength, Vitality, Dexterity) at 59 and 60.

Level 35:
Here it is, Memorial Day. I have finally finished the end of my Arnika grinding.
All four specialist casters have learned all of their spells, 36 or 37, to be exact.
Every attribute is above 60, being a human party. The Bard and Gadgeteer maxed Strength, Dexterity, Speed, and Senses. They have Vitality at 62, and Intelligence and Piety at 61 (these are base stats, before equipment).
The casters maxed Intelligence, Piety, Speed, and Senses. They have Vitality at 62, and Strength and Dexterity at 61 (they wasted no points in Intelligence above 95, waiting for Powercast to be unlocked at the Trynton well).
Relevant skills are all maxed, as well.
Melee: The Bard and Gadgeteer maxed Close Combat, Sword, and Shield (Light Swords and Light Shields will be farmed later on). The Priest maxed Close Combat, Mace and Flail, and Shield (Mauler or Diamond Eyes, with a Light Shield). The Alchemist maxed Close Combat and Staff and Wand (Staff of Doom). The Psionic and Mage are too weak for melee combat, and the SOD is taken by the Alchemist.
Ranged: The Bard and Gadgeteer maxed Ranged Combat and Bow (Tripleshot Crossbows). The four casters maxed Ranged Combat and Throwing and Sling (Wrist Rockets).
Magic: The Bard maxed Music. The Gadgeteer maxed Engineering. The four casters maxed their respective spellbooks to 125 (with their 25% class bonus). All six realms were maxed, with the exception of the Alchemist having no Mental realm.
The Bard and Gadgeteer maxed Powerstrike, Reflextion, Snake Speed, and Eagle Eye expert skills. The four casters maxed Powercast, Iron Will, Snake Speed, and Eagle Eye.
Mythology is maxed for everybody, having fought so many battles. Everybody has Artifacts to at least 75, which can be increased later with using Mana Stones. The Bard has Communication at 78 (97 with the 25% class bonus).
This leaves the Gadgeteer with her Locks and Traps at 76. I tried playing with the Arnika Bank 8-tumbler lock for half an hour, and this didn't work. I believe that Locks and Traps skill increases are on a timer, so you have to save and reload frequently (hopefully you don't crash the computer). The reason I ask is because there are not enough treasure chests/locks to get to 100 Locks and Traps in a normal game, and I don't want to be casting Divine Trap at every chest.

Did you know you are incredible? Your devotion to this game is awe inspiring. I have so enjoyed following your exploits.

Thanks a lot. This was almost two years of work to get a "perfect" MDP (a lot of beer for the long grinding nights).
My party is still not "perfect", however. I'm currently playing around with the Arnika 8-tumbler lock, trying like crazy to get my Gadgeteer a Locks and Traps skill increase. I'm experimenting with saving and reloading, turning off the game and restarting it, and 24 hours of resting.