i just use the window gadget gpu observer. theres also one that comes with trixx
The problem with the trixx one is it doesn't work for 4+ gpu rigs. It doesn't show every gpu. It also is super tiny. I assume the gadget one is some what similar.
I didn't think the Windows version of the catalyst driver supported more than 4 GPUs, does it now?
As for viewing temps etc in Windows: GPU Caps viewer.