From what I see, you're using an aftermarket gpu cooler, which is good. Temps still seem a bit high, like you're using a stock hsf; might want to repaste the gpu and reseat the gpu hsf.
Also, your rig is AMD so 'cool 'n quiet' may be enabled in the BIOS; this throttles back your cpu when it gets hot (I believe), so disabling it may help to keep clock speeds normal at the cost of a bit more heat. Of course stress testing runs the cpu hotter, so hopefully your cpu hsf will handle it.
I would disable the 'cool 'n quiet' first, if that doesn't help then try repasting/reseating the hsf.
TJS
(I don't need to put a disclaimer in here, do I?)