It would be hard to get much past the low fifties for character level, without cheating or running into a bug with
experience bombs.
I finished the game at level 53, after;
[*] maxing Wisdom, which can give you one extra level, maybe 2; see
here[*] using the Resurrect/leave/return/re-kill trick a bit in Iona's dungeon to level up, and randomly in the sewers and Dark Forest looking for more dropped charms
[*] completing all quests and killing all hostile creatures (except some at the very end, near the Demon of Lies dungeon)
[*] also, there are a couple objects in the game which can raise you up a level, which I left until late to get the most experience points from them