anything above a 6850 will face serious bottleneck from cpu.
i don't wanna say but some serious noobish talk is going on.
I have the same processor, and my 6870 doesn't bottleneck at all.
I told him he'd get a bottleneck with the 6950, he refused to buy it, now he goes with an even more powerful card like GTX 570 that will bottleneck even more.
I just stopped posting after that.