I'm surprised there is no performance hit in Unreal 3. You would think that since the GPU has to handle both graphics AND physics that the fps would take a hit. Apparently the opposite is true. You get a 2x to 3x fps boost by have a gpu handle both tasks. GPUs are truly powerful (and apparently underutilized by graphics workloads alone).

PS: I could probably build a Phenom, 780a based system that would rape an ATI system in these few PhysX games. Sure, that wouldn't make much sense but it would work just fine LOL.