The gtx 760 is marginally better than the 7950, and a little more so when overclocked. However, there are still many situations in which the two cards will end up in a draw or the 7950 coming out a little ahead. Personally, I would go with the 760, as it will also produce less noise/heat and use less power.
Here's a quick basic framerate comparison between the two:
http://www.anandtech.com/bench/Product/854?vs=855
Also, the fx 8320 is compatible with the gtx 760. Any cpu is compatible with any gpu so long as the motherboard has the appropriate PCI-E slot (and yours will, don't worry).