https://www.hwcompare.com/12351/gefor...adeon-hd-7970/
Radeon HD is better at Power Consumption and Memory Bandwidth
2 GB GTX 680 is better at Texel and Pixel rate
GTX 680 is 700$ on Amazon
Radeon HD Is 399$ on Amazon
The Physx for Nvidia might not be used for every game, it's only used for a few, but it's actually good for the games it's used for
So for my opinion, get the Radeon 7970
Note : those are the prices for only 1 video card
I hope I was able to help