If you're just going to be doing gaming, get a 7870. If you're going to be design work and rendering and stuff too, get a 660 Ti or a 670.
You've got a 750W Corsair PSU haven't you?
OK. Are you just doing gaming?
I'd advise you go for a 7870 or a 7950 then.
Get an i5 3570K and a Gigabyte GA-Z77X-D3H and I say it's good.
Stick with the i7 if you want, but get that Gigabyte board over the ASRock.
Ok a couple of points.
CUDA is also used in Physx so if you are planning on gaming with Physx games its worth it. Also if you play on using CS6 for video editing (3d or HD), its worth it. Also, i frequently use nearly 16GB of RAM when video editing or using virtual machines. If you do either of these things you need to factor that in.
Secondly, we need to know what size monitor (resolution) you're planning on playing at, if its low, then the CpU will be the important factor (and GPU may be overkill) and if its high, the GPU needs to be able to cope both in a processing and a VRAM sense.
As I said, 1920 x 1080
Well, the higher the better really, though I'm fine with sub 1080. Psu is corsair 750
No, what you said is this...
Quite different.
If you're going for 1920 x 1080, then you don't need anything close to some of those gpus, as they will provide above 60FPS. IF the monitor you wish to use is a 60Hz one, then you're wasting your money.