I've red about the experience cap remover, this means basically that you can go to higher levels but are there any benefits with it. There aren't any spells you can't cast??
Could someone tell me what the benefits are (doesn't matter which class).

U can get a lower thaco . im not sure whether a mage will be able to cast level 9 spells but i think so.

I am a sorceror at the highest level, I got a very high intelligence and wisdom, so I am already able to cast 9 level spells, but what I meant is that there aren't any 10th level spells as far as I know

There are no 10th lvl spells in the game, so what is the point of being able to cast them? And the spell book only has 9 pages to it.

Officially the game's scripts support character levels up to 40. However, most advantages that come with levelling up dwindle and die from level 20-25; for instance, at level 20 a mage will have 2 mem slots in level 9 spells. At level 40, a mage will still have 2 mem slots in level 9 spells.

Incidentally, intelligence and wisdom have no effect whatsoever on how many spells you can memorize, it's a set amount as per your level, and neither mages nor sorcerers start getting mem slots in level 9 spells until level 18. Level 18 for mages and sorcerers requires 3,000,000 XP, unattainable in BG2 without removing the XP cap. Meaning if you have level 9 spells, you already removed the XP cap (and somehow levelled up a LOT). Or you cheated, one or the other.