Also running a 2500k at 4.2ghz with hyper 212 evo.
So the problem is, i'm actually lagging in diablo 3(haven't played anything else on it yet, just finished build two days ago). Like i get 5 second game freezes(i can move, but enemies don't. Usually end up dead but the time it catches up). Had some trouble with it only wanting to run motherboard graphics before but i think(thought mabye) i had that figured out.
sounds like a server problem rather than hardware. The connection could be unstable, since you yourself is able to move and not the enemies. You could try to reinstall it to fix it but blizzard games tend to have these problems. I remember D2 had that problem and that was because of internet connection problems.