Advice and opinons on proposed build

Hey guys, heres my current build. (2-3 years old, my first build.)

CPU: Phenom II X4 965 BE
MoBo: Asus M4A79XTD EVO
GPU: Saphire HD 5870
Memory: Xms DDR3 2x2GB 1600 cl7 Corsair RAM
PSU: 750w Corsair XT
Windows 7, 64bit

I was originally going to upgrade the RAM to 8GB and the GPU to a 7850 for Far Cry 3. Then i figure out the performance increase would be slight at best and I'd have to change card again fairly sonn and i settled on a 7950.

But now i'm thinking i might get longer out of a 670. My question is:

Is the exta money worth the better performance i@ll get out of the 670 and how long (roughly) will i max games at 1920X1080?

Also if the 670 is the best solution could you recommend a 670 card from these two pages.

http://www.dabs.ie/search?q=670

http://www.komplett.ie/Komplett/site/SearchResult.aspx?...

Thanks in advance