I used the same heatsink with the venice "xp-90", my temps on the Opteron are 36-37 idle and 53 after a couple hours of Prime95, two instances running in-place largeFFTs.
EDIT: I initially test for 2 hours then overnight when it's convenient. The overnight temp was the same.
My GTS is 600core 800mem.
My venice and opteron scores: