If you're playing at low resolutions, then the cpu, maybe could be a little bottleneck, but if you're playing at 1080P with high refresh or 1440p, then I'm thinking you're CPU is not an issue. If you have a decent overclock, that's still a pretty decent CPU for gaming.
Intel hasn't done anything really grand with their cpus since Sandy bridge(which you have), every generation post, has only managed small percentage gains in performance increases.
One way to test would be to check CPU usage rates while gaming, if they're maxed, then you could think about what next, but if you're not maxing cpu usage, you're not in need of an upgrade.