mmm... they perform on par mostly if not always the GTX260 takes the cake, in performance what you have to consider are detail especially price, EVGA, Temps, Power Consumption, etc, just EVGA step up its enough for me at this point but, in Ati Favor and since i own a 4870 instead of a 260GTX, the Ati card offers better image quality for some reason when watching movies and 7.1 Audio...
mmm... physx or CUDA i wouldn't buy based on that, since at some point Havoc will also become GPU based and probably the Physics Standard Microsoft owning both Dx an Havoc and a big chunk of my Country LOL...
To conclude Buy the cheapest if they cost the same buy the EVGA 260GTX