Your CPU is still great to run modern day games just fine. I am still using an even older CPU than yours a Core i5 750 at 3.6Ghz and it rarely a bottleneck to my overclocked Radeon 7950. If you feels need of faster gaming performance simply upgrade your GPU to a newer one. I recommend you to wait until AMD releases Polaris that would offer you considerable boost in gaming performance while still consuming similar power to that of your current 7850 thanks to Polaris being a next gen architecture at 14nm process.