For 6 months I have been running 2 o/c GTS450's in SLI on my 2500K setup. Just got a GTX560ti from a mate who moved states, and want to use one of the 450's as dedicated PhysX. Would I need an SLI bridge on them or not?
You don't need a bridge, just dump it in and boot up. Once in windows open up forceware control panel and set the gts450 for physx and the screen will go black two or three times and you are done. Don't even need to reboot and it will provide a nice boost in games like mafia 2. It did for me when I was using a 8800gt for physx alongside a gtx460.