Some users have recently had their accounts hijacked. It seems that the now defunct EVGA forums might have compromised your password there and seems many are using the same PW here. We would suggest you UPDATE YOUR PASSWORD and TURN ON 2FA for your account here to further secure it. None of the compromised accounts had 2FA turned on.
Once you have enabled 2FA, your account will be updated soon to show a badge, letting other members know that you use 2FA to protect your account. This should be beneficial for everyone that uses FSFT.
In Cryostasis at 1920x1200, going from tri-SLI with 285's to SLI + dedicated PhysX bumps you up from 58fps to 75fps (one guy trying it both ways on the same system). Similarly, with a 295 for graphics, going from a 9800GTX+ to a 280 for dedicated PhysX gives you about 10fps (two different guys with similar setups).
You can but its a huge waste of money. Practically speaking it doesn't make a difference right now. Maybe in the future it will but Mirror's Edge and Batman Arkham Asylum won't see much benefit from using an uber card for physics computations.
I use an old 8800GT for Physx along with my GTX 285 for video, and it works perfectly. The only thing I hate is how much noise the damn fan on the 8800GT makes, but that can be fixed with an aftermarket cooler.