The CPU performance should be fine. If you still have doubts and want to test this, then try playing a game at a few different image quality levels. If the framerates are close/similar between settings A and B, then the CPU might be a bottleneck. But if the framerate is noticeably different between settings B and C, then the GPU is the bottleneck. For most games released in the past few years you should be able to raise settings high enough to ensure GPU bottleneck.