The guys at hardspell.com have tested a system with a Radeon HD 3850 for the graphics rendering and a GeForce 9600 GT for the PhysX:
They used the oZone3D.Net PhysX FluidMark to compare CPU PhysX (score=759) and Hardware PhysX (score=2909). This is the proof that Radeon and GeForce can work together for a better gaming experience!
The functionality of CUDA and its implementation of GPU-accelerated PhysX processing has benefited many a GeForce user. Users of ATI accelerators lacking this incentive either use Ageia PhysX card or avoid it altogether. It has been verified by Hardspell that in an environment where Radeon accelerator(s) do graphics processing, a GeForce accelerator can be used standalone to process PhysX. Hardspell used a Radeon HD 3850 along with a GeForce 9600 GT on the same system with the display connected to the Radeon, though no form of multi-GPU graphics connection existed, the GeForce card partnered the Radeon well in processing physics, while the Radeon did graphics. Results of the oZone 3D FluidMark, a benchmark that includes routines to evaluate the machine’s capability in processing physics, showed a greater than 350% increase in scores, showing that the GeForce accelerator is doing its job.