mister g said:
Not really, if you use SLI then all cards are slave to one. But the connection means two cards share resources, you still can't dedicate just one to PhysX though. Quad SLI 295? Do you happen to live next to a nuclear power station?
Actually, you can dedicate one to PhysX.
As for what card to use for PhysX? IMHO, it's not worth it, but I remember seeing some benchmarks saying that there's no gain from using a high end card for PhysX. A relatively low end card (GT240 for example) will run just as fast.