Originally Posted by
tuggyne
How does that even follow, though? I mean, how would you fluff that? "Sorry, your spellbook won't hold any more of that level"? "Nope, you totally can't figure out any possible way to use pen, paper, and special inks to further expand your repertoire, which is actually sharply limited by your memory, despite being notionally contained outside it"? In any fix, it's important to avoid breaking fluff in bizarre ways just to satisfy balance concerns.
I'd also note that this specific formula prevents any wizard from learning 9ths until they have a bare minimum of 42 Int, even though they can cast them at 19 Int. Similarly, 8ths are available only at 38 Int and up; 7ths limited to the exclusive 34 Int club; and so forth. If the goal was stealth-nerfing high-level spells, I suppose you've succeeded, but unfortunately it's not as effective against certain high-op techniques, leading to uneven nerfing in precisely the wrong places. That is, you're basically putting up a "you must be this cheesy to learn ninth-level spells" sign.