Yeah Windows sucks for SMP folding.
I think you ought to get 550k PPD on average with Linux. And that system will be pulling like only 450W from the plug. If you're a little lucky with the WUs you might even crack the 700k PPD...
Especially if you raise the BaseClock one or two MHz...
But check again in terms of CineBench. I don't know if you noticed but you used only 32 threads running CineBench too...
By the way: Ubuntu Linux installation + setting it up for F@H is like 20 minutes. It's really easy, and you don't even need a fast SSD or something. The client creates a RAMdisk to run off... I'm there whenever you need me to quadruple your PPD in terms of SMP folding