with much respect to the previous post, bottleneck does exist. Try pairing a celeron (or something slow) to a high end card, i know it's an exaggeration but it's just an example.
2500 is decent (i have a 2500k @4ghz), and usually games tend to use the GPU more, in effect having the gpu @~100% usage while the cpu is not at 100. For example, on bf3 multiplayer, my 4ghz sits at around 70% while my 670 is already at max utilization. And bf3 loves cpu. So for my part, the GPU is the bottleneck. But its ok since i cannot afford (or dont want to spend more) for a gpu