Found a way to gain infinite xp: I killed the healer Thelyron after I dispatched Braccus, to punish him for his deeds. Interestingly enough I discovered that I could revive him, and kill him again. This gives 3000+ XP with each kill, he also does not fight back.
This probably also works with other revivable NPC's but I can't verify right now, since I don't have time to play.
