I just checked my current MDP, and found that not all of my level 34 casters could cast level 7 spells at power level 7 with a 100% chance of success.

Priest:
Falling Stars-No
Death Wish-No
Restoration-No

Alchemist:
Tsunami-Yes
Death Cloud-No
Earthquake-No

Psionic:
Prismic Chaos-Yes
Cerebral Hemorrhage-Yes
Mind Flay-No

Mage:
Nuclear Blast-No
Asphyxiation-No
Concussion-Yes

It seems like the cheaper spells (in terms of SP cost) can be cast at PL7 safely, typically the ones only at thrown range, or the ones that only affect a single target. The "hit all enemies on the screen" spells typically can not (except for Prismic Chaos, which typically does annoying things, like making enemies blind or afraid, making enemies run away, and making combat last longer than it should.)

It just seems like a slap in the face, that a specialist caster would have 125 skill in their spellbook, and 100 skill in their appropriate realm, and be level 24 or greater (eliminating the level penalty), and still not be able to cast level 7 spells at PL7 with 100% certainty.

This gives more credibility to Bishops, in that, 100 isn't that much different from 125 in their spellbook skills.

Looks to me like the devs had found the sweet spot for the algo,
how boring would it be if you could cast SL7 spells at PL7 e.g. just one level after you can learn it,
or to never be able to cast it on PL7

Think at lvl 38+ your PL7 dot is almost entirely green if all other values of caster are maxed

Try adding the Cap of Wiles to the mix, and see if you can make Mind Flay's status become Yes.

For all those other "No"s, excepf for the divine ones, you could try hunting down those -mancer enemies (like Aeromancers), and try to get them to drop their rings. Maybe that might be enough to get many of the other spells to "Yes"?

Basically, if you get your Realm skill to 110, that might be enough, and if it isn't, you could get another ring to raise it to 120.

@townltu: It seems to me that a specialist caster should be better than a Bishop at their particular brand, giving a 100% chance of success with level 7 spells cast at power level 7. The Bishop should have light green in thieir circle, with a small chance of failure, due to the fact that they're an all-around caster. I don't know where you got that "38+" number. AFAIK, specialist casters top out at level 24, with no hope of level 7 spells at PL7 (at least the good ones).
@dtgreene: That seems like too much work, and the specific items you mention only affect one realm (remember that there are only two slots for extra items, like rings, and you probably will want them filled with better items than a ring which helps only one realm anyways).

Cap of Wiles doesn't use the ring slot. Plus, it does have a reliable location. (It is cursed, however, but by this point you can cast Remove Curse if you want to give it to somebody else, though in your MDP only your Psionic cares about that bonus, anyway.)

Also, if one ring is enough, you can just choose which spell is more useful to be able to reliably cast at PL7.

(Is a single Aeromancer's Ring enough for Asphixiate/Death Cloud? Those are the most expensive spells whose realm skill can be boosted through equipment, since there's unfortunately no such item for Divine Magic. (That might be a good idea for a mod; add some holy symbol accessory for Priests (perhaps only Priests?) that boosts Divine Magic and perhaps provides a few other boosts; maybe have it cast Turn Undead when used as an item.))

I would just think that the bonus for a specialist caster would be to cast his/her level 7 spells at power level 7 with 100% success. That would be the advantage that one specialist class would have over a Bishop.
The Bishop is all-around a great caster, not too skilled in any one spellbook, so I could see giving him/her a more limited chance of success.
But I digress. Besides, the diving gear, or whatever you call it, takes up one spot underwater, so you probably will want to have a good item in the other slot, namely, an Amulet of Healing, so the character carrying the Staff of Doom doesn't die.

Underwater is an extremely small portion of the game.

Furthermore, if you have a mage using the Pyromancer's Ring, you can replace that with the underwater dear, since fire spells don't work underwater.

Also, level 7 spells at PL7 aren't *really* necessary, to be honest.

I know. I find myself casting level 7 spells at power level 6 just to avoid the possibility of a fizzle (thankfully, no backfires).