Differences in Lethal vs Non-Lethal completion of missions?

I have played the game completely through and I am wondering if there is any difference in the way you complete a mission. If you do it completely unseen do you get any sort of offset in XP for all the missed take downs knock downs? Does it have any impact on the story line like

Does it alter the scene where you save Jacks and he sees you kill all those people if you did not kill them?

I guess I am wondering if there is any replay added to the game other than personal challenge if I were to try a completely stealth/knock down only play through vs my last one where leaving people standing just appeared to give me less XP.

Solution 1:

From personal experience and from scrounging around the internet I come to this conclusion:

It does not matter if you kill everything in sight or knock them out with your baton. It also doesn't reward you with extra XP, if you go unseen and don't touch anyone (I think you even miss XP, if you do missions that way).

The story is pretty much scripted.

Saving Jack non-lethally doesn't change anything. The same cut-scene rolls anyway, so just go guns blazing.