In Divine Divinity quests gave more experience at higher levels. By killing opponents first and then turning in quests you got more experience from both, compared to the other way around.
In D2:ED/DKS the quest experience is fixed, but opponents still give more experience if you are at a lower level than them, and less if you are higher. If you level up by turning in quests and then go kill opponents, you will get slightly less experience than clearing the opponents first. It isn't a huge difference, though.
