GTX 770 or HD 7970 and will pci 2.0 bottleneck a pci 3.0 card?

The title assays it all. I'm looking for a new card. Which is better? And will pci 2.0 bottle neck a pci 3.0 card?

The 770 ans 7970 trade blows and are about even. The 7970 has more computing power, so mining bitcoins and such is quite nice on the card. Also you have to look at CUDA vs. OpenCL which depends on what programs you are running. Personally, I would choose the 7970, because It is cheaper at the time and I personally prefer AMD over nvidia. One last thing the 770 is a newer card, which may be better for you.

As for you PCI question, neither of the cards will bottleneck in a 2.0 slot.