I just built a new system and I was wondering if there would be any benefit of using my old 9800 GTX in my new rig as a Physx card. I know not many game engines support this, but it would be better than just shelving the card. Is it worth it, or would it just be a waste of power and extra heat in my case?
With that setup it's probably not necessary. You will still get good performance in just about any physx game with the GTX 570 handling both graphics and physx. Better to shelve the 9800, unless you almost exclusively play Metro 2033, Batman, Mafia 2, and/or Unreal Tournament 3.