If you're into gaming, what you're looking for is a good GPU set-up usually. That means having a powerful high-tier GPU (these days, it's 280x/290/290x for AMD or 770/780/780Ti for NVidia) and the rest of the hardware good enough to support it. Most likely, on single-GPU systems, an i5 and 8GB of RAM (CL9 1600Mhz), a good drive and a decent motherboard will last you between 2 and 4 years with a GPU of the kind stated above, depending on your resolution, on how much you're willing to sacrifice detail for framerate and on how technology evolves.
Anything higher usually starts going into more particular needs, like video/image editing, 4k or 3D gaming, 120Hz+ gaming, or ultimately Multi-monitor systems. In that case, an i7 might help more than an overclocked i5, but you'd also need a Crossfire/SLI system to be actually able to run all that.
So yeah, If you want some future-proofing for your single-GPU rig, a 770 will help WAY more than a i7 would.
Also, if you're not into PhysX, or any of all that silly useless eye-candy NVidia likes to put in every game they get their hands on anyway, I'd consider an ATI GPU. A 290 (non-x) would run close to a 780 for at least 50$ less, depending on partner brand and the place you're buying it off to. Mind that, if you're buying a 290, you're going to need that 750w PSU although...