I have always wanted to try a 'hybrid' AMD/Nvidia setup, as I heard it was possible to have an AMD Gpu and still use an Nvidia card as Physx addon (with the right combo of drivers/bodges)
Having said that, my current GTX260 is rather hot and bothered - I have left the side of my case (the one that has no fan on it) off, with a 20" floor mounted fan pointed at it
Or maybe get rid of it altogether after the 'experiment' and get another AMD of same spec; the motherboard only supports Crossfire, not SLI. Or, or, or hmm umm, have the Crossfire AND Nvidia Physx combo (if I could manage to do it without screwing the whole PC up lol)...
Anyhow, I'd be interested in benching the various permutations, especially with Phsyx games like Mirror's Edge and Batman: Arkham Asylum, running on modest, fairly old hardware (Core2 Quad)...