the memory bendwidth being different 256 bit on the 1 gig, 192 bit on the 768
i think the 768 would not be bottlenecked at all, and the 1 gig might be slightly (nothign a small overclock wouldn't fix though) also the bottleneck would be slight and onyl effec tperformance by a small margin really you're good with either card
Thanks everyone for your support.
Now i get that my GPU will be bottleneck to very small extent n i may neglect it.
I am gaming at 1280 x 1024.
N i am going to buy 1GB wit 256-bits of memory bandwidth.