My friend is looking at a cheap upgrade to get a little more physx action from his setup.
 
He is running 2x 8800GTs in SLi on an XFX 780i mobo.
 
If he was to get a 3rd 8800GT or even an 8600GT and use the 3rd slot for physx, would it work ok?
 
I know that 3x SLi on this mobo would drop speeds back to 8x instead of 16x, but would that factor in if the 3rd card is just doing physx?

I honestly don't know, but in my experience running two GTX280s in SLi, dedicating one of them to PhysX never really made much of a difference compared with just running them both in SLi. I think he'd be far better of selling his 2 8800GTs and getting a new single 460 or 480.

" @Binman88: What should he expect to get for 2 8800GTs you think?  I thought that would be a better plan too. I'm not a huge fan of SLi, but I don't know everything about it either. "