Generally speaking you'll want a Core i7 to stream. So 7700K or 6700K are your best bets. Streaming requires extra CPU resources and the i7 has hyperthreading which gives 4 extra threads. The i5 lacks hyperthreading and has 2MB less L3 cache. You already have a Z motherboard. So you can update your bios, get a 7700K, Overclock it to 5GHz, and stream happily. Though the newer i7 8700K is much more suited toward streaming with its extra 2 cores.