I just got mine GTX480 yesterday and PhysX seems to be working perfectly fine.
I guess it doesn't answer your question,but I am fine with "just" GTX480:)
Yeah, your right. And the GTX 480 is a gaming card plus a work station card. And with the power of Fermi and 480 Cuda Cores (low-end supercomputing level) it should not even break a sweat when it comes to the PhysX computations.