I'm looking to upgrade one of these to make the game run better.

The reason why i'm asking is I have an intel CPU, and I've heard that Nvidia cards (gtx) run better with intel CPUs, and that the same goes for ATI and AMD. Normally I'd call BS but, I heard this from fairly techsavvy friends.

My specs atm:
CPU: intel i5-750
RAM: 4GB
GPU: HD 5570
win7

Currently I can run the game fairly high with quite a few features turned off at 1920x1080, but it constantly dips between 20-30 fps, which is unenjoyable imo.

So any tips? I'm leaning towards the 7870 because it seems like a better price-quality ratio.