QX9770 should be fine for a 5970 assuming you enable AA and AF. After all, at lower graphic settings, the CPU is more likely to be the bottlenck
I swear, I have no idea where people get this stuff; the CPU is more of a bottleneck at lower resolutions only because the GPU is doing comparitvly less work. A CPU does more work at 1920x1080 then at 1600x1200 or 1024x768, but the GPU does less work in comparision as resolution lowers. To argue that a CPU does more work as you lower resolution is insane.
And no, a QX9770 won't be a bottleneck for anything except MAYBE SLI'd 480's/CF 5970's...