I5 4670k will do ok but depends what games you plan to play and at what resolution, Hz and frame rates.
BF1, Ghost Recon, FC5, Devision, Gta5 to name a few can chew i5 4c 4t CPUs running high frame rates. 6th gen i5s are having trouble also.
4c 4t CPUs used to be all you needed but now with games taking advantage of Hyperthreading and more cores, i7s are very handy. Especially at higher frame rates where more load is put on the CPU. More working threads helps reduce the chance of running a CPU bottleneck of 90~% where the GPU wont perform as well.
Overclocking an i7 4770k or 4790k is a good plan if you don't intend to overhaul to keep you going until pcie 4/5 motherboards are rumoured for release late next year / early 2020 +...