i wouldn't consider 28fps playable to be honest. Anything over 35fps is smooth sailing. But the stuttering i suffer with Physx switched on still happens even at 1680x1050 which is a considerable res decrease and still the problem persists.
The VRAM of my combined cards is quite high 2.6gb approx. Should be more than enough to run the game at max even with physx ON. I can run Mirrors Edge and Batman Arkham Asylum at max and those games are both Physx enhanced and work no problem.
I just dont get why Cryostasis wont work like that when physx is on