Mafia 2 will utilize PhysX and 3D Vision

[Carfax]

^ so your saying i need to spend 100$ on a spare gpu, to enjoy 2 games that combined cost 100$?

You don't have to.

You can run PhysX on one GPU, if it's powerful enough to do both that and rendering.

I use a dedicated card purely because of the performance benefits.

And if you have enough money for a hexcore processor, then I doubt 100 USD will be much of a concern.