Just tested the DD 480 wb on one of my 580s.
I had to use pads on mem instead of TIM, GPU is a few mm higher on the 580.

Result from a quick run at 850/2100:
Temp while running MSI 'multiGPU DX11 path' combustor was around 50-60+C on the back of the water cooled card, even around the VRMs.
GPU monitor at 55+C.

The other 580 (with OEM h/s) had board temps around 75-80+C... and GPU temp was almost 100C+.

Probably not as good as the 580 block, but good enough for me...

Now on to the 2nd 580...