An i5 6600k will be more than enough but if you plan on upgrading your GPU/future proofing then an i7 will have more room for improvement with multi-threaded games and future GPU's etc. With a GTX 970 at 1080p you will struggle to get an i7 6700k over 50% load.
so like watch a person play twitch while gaming? a i5 should pull that off, one important thing to account for is internet speed, having a multiplayer game and a stream going can really eat up bandwidth. or you could always look at 4790K prices.
An i5 6600k will be more than enough but if you plan on upgrading your GPU/future proofing then an i7 will have more room for improvement with multi-threaded games and future GPU's etc. With a GTX 970 at 1080p you will struggle to get an i7 6700k over 50% load.
Go with the i5, the k and an aftermarket cooler if you want to overclock, the i7 will be a waste of money unless you're rendering with that graphics card.