are you running in windowed or FS? are you running at max settings?

in my experience AMD does not cooperate well with nvidia cards, but that's more biased personal preference i think. it looks like all of your pieces are working well on their own, but when put together something weird is happening.

have you checked voltages?

I prefer furmark to 3dmark for stress testing. a lot of times i have no problems in 3dmark but will crash on furmark.