How good of a graphics card would i need for just physix?

Just kind of thinking out loud here. I'm planning on getting a 7970 but if i want to run physix i would need an nvidia card right? How good of a card would i need for that. Basically how cheap of a card could i get to just run physix?

Some games will support physx with a ati card but the preformance is nothing comapred to nivida. A great card that is around the same price as a 7970 and preforms the same is a gtx 670. 

How cheap you can go and how cheap you want to go are two different things. Anything from a Geforce Gt 520 and up will support physx and some older models. 

For gaming a cannot recomend anything below a 550 ti or 650 ti. That is nividas basic entry level gaming card. For the best physx preformance you want to pick a card with the most CUDA cores.

You can not run a Nvidia GPU with a AMD GPU even for just the use of phyx's. I've seen very few people acomplish it and its a driver nightmare. If its borderlands 2 you want to play, just do the CPU hack. Someone else posts it, he will show up shortly im sure.

Just use your CPU for the 3 games that actually use PhysX

I wonder if something like the 8350 would be good for something like that. I wish i had money to buy all kinds of stuff just to test it.