I like it to level up as slow as possibly, but in fact, being a lower level further into the game (and main quest) give even more XP for killing, so ...
Teh Priest build is still a challenging battle ! If a Black Ring Battle Mage with a warhammer doing a rush attack on me he can kill me very fast if I'm no alert enough ! Sometimes I haven't the time to use Blind or Charm ... because his attack is so fast !
But I never take the extra XP reward by quests and I don't invest in the Wisdom skill, don't invest in the Mindreading skill (to lower or even stop the XP depts) and don't make use of the respawing enemies in Keara's Fortress ...
For me no need to level up as fast (or high) as possible in a RPG.
