Most games won't use more then 4 cores, at the moment there is no real need for an i7 for gaming. Better go for more ram if you have "only" 8 gb. The i7 6700k would become (light) bottlenecked by your GTX 770 anyways.
I would not upgrade from an Ivy Bridge CPU. In fact, with low level APIs coming into the spotlight (DirectX 12 and Vulkan), CPUs will become less and less important when it comes to gaming.