[Lazortag]

This is really easy to test. There's a level 50 guard with low HP in Innothule, all you have to do is have a level 1 swing until he does 1 damage, then have a high level character apply a lethal dot, zone, and the level 1 should get the kill.

I'm pretty sure you can go over any exp cap there is by going in a zone with an exp modifier, or if there's an exp bonus or something.