The i5-6600 is lga1151 v1. The i7-8700k is lga1151 v2. Same pin count, but different socket. It's not just a cpu upgrade, you'd need a whole new motherboard too. The best cpu upgrade, for just a cpu, would be the i7-7700k, and thats if you have an unlocked motherboard, otherwise you'll be just the same with an i7-7700. All that does is open up 8 threads vrs your current 4, which can be a decent amount of fps in some games, and for streaming, but otherwise it's pretty similar in performance.