Help with upgrading my GPU.

[Vokilim]

I want to get a new GPU my Radeon 6950 Ice Q X Turbo is kinda kicking the dust and not holding up super well to the newest games like Wolfenstein: The New Order. I need something new, and im not sure what to get. Here is my current build, I think the CPU is still pretty good? Please tell me if i'm wrong about that though. Ideally, i would like to only upgrade the GPU. Open to other suggestions though. The most important thing i guess would be will my PSU be able to power it. AMD or Nvidia, does not really matter I would just like a reason why i should buy it over the other. I was looking at the GTX 780 (how big is the performance gap between it and the 770?), I'm not sure if that would work with my setup though.

My build: http://pastebin.com/MAFK2YFk

 

[Unolocogringo]

There is about a 10% performance difference between the 770 and 780.
You power supply has 52amps on the 12vrail. Which would be fine for either card.

The rest of the computer is fine you will have no problems with bottlenecking for either card.