Unless you did an insane amount of resurrecting, it seems killing high level monsters early has more of an effective than I thought.

I did a moderate amount of resurrecting my first game, and finished at level 53. I played a bit when I first tried it, and then used it to make sure I went up a level before getting a level bonus, to maximize the effect (one bonus is in an area where you can not leave to level up and come back to it).
I explored everywhere, did all quests and put off the level bonuses until late in the game, but did not pay particular attention to either the combat or quest character level dependencies for experience. Without spending a lot of time resurrecting creatures, I can not see finishing higher than the low fifties (most common is in the mid forties to low fifties).

Except for a relatively high number of Experience Bombs (or a glitch with one), a final level of 59 or 60 would seem to be attributable to re-killing high level opponents for the larger experience reward.