If you look at pure specs the 7850 is ahead of the 650 Ti Boost (http://gpuboss.com/gpus/Radeon-HD-7850-vs-GeForce-GTX-650-Ti-Boost), and Physx is used in less than a handful of game titles also considering that AMD has Mantle (which is gonna be quite a game changer pun intended :)
I'd say go...