Any modern CPU can pretty well handle physics without any slowdowns or affecting fps. All it takes is some multi-core optimizing, with Octacores CPUs coming, games are barely taking advantage of 2 CPUS, that's really really Sad but good for GPU makers. GTA graphics are badly optimized because it was ported from consoles. Best games never used PhysX on my book. Crysis, Stalker, MW1/2, NFS , Unreal 3 had physX in only 1 map and the physx rain was really really annoying during gameplay.