Rubn_alq :
BTW bottleneck appears when your CPU can't use the full power of the G. Card.
To be a bit more specific, a CPU bottleneck appears when your processor is having greater difficulty coping with its workload than the video card is with its own workload. A slow processor doesn't intrinsically have any problem "using" the full power of a video card, its just that it may hit a wall doing its own thing and impose a limit on the framerate before the GPU does.
I really don't think I'd worry about it. CPU bottlenecks are extremely game-specific and unless you plan to upgrade your CPU you're stuck with what you've got anyway. I think most low- to mid-range cards are a reasonable choice as long as you're power supply is able to keep it running.