Based on points, SMP on the C2D is the most productive folding client. For that, native Linux SMP > VMWare Linux SMP > WinSMP.
I had heard fairly definitively that GPUs require enough babysitting from a CPU core that the core is essentially tied up in terms of folding.
I must say that I am very happy of my point put out with my C2D. Not to jack the thread, but doesn't a PS3 pump out more points than SMP with a C2D