I just got my 6400hz g.skill in today, they have the black pcb, not sure if that matters, but they seem to be great so far.

I was running 4-4-4-4 @ 1040 with 2.3 v, but i did some reading and i am afraid to run any more than 2.2v to them if it is going to start making them worse at oc'ing and not make them as stable after some time.