I am talking in general tarek. Hell i bought a psu from a certain "micro" store with 2 weeks warranty. Am saying outside lebanon where companies have warrenty, not lebnon.
Well rorosas, since my pc is proportional to urs, dual core + 460, id get a 670.
Here is why, 7970 pushs pixels/textures/mem bandwidth/compute...etc alot more than 670. So the bottleneck,aka loss of absolute performance is more. You save 50$s/or get a nonreference card (recomended cards above).
Let me tell you bout bottleneck, u look at games benchmarks with ppl having higher cpus i5s and up (probably oced too) you will notice that ur having lower avg and min framerates. But ur experience will not change because ur already have a powerfull card. So if a 670/7970 performes 80% of its absolute performance your still pushing great fps.
Here is a performance comparison between old i3 and i7, you can see the difference isnt great. And the difference is almost same between new i3s and i7s..etc :
http://www.overclock.net/t/943540/i3-vs-i7-gaming-performance-updated.
As u can see instead of having 80 fps u will have 50, and thats in the severest case. And the card is 6970 so u will have more fps. I can bench a few games for u but its gna take me forever since am "updating" bf3 with the 5g patch >.>
