Yes you dont need to change motherboard from i5 6600k to i7 6700k. they are both in socket lga 1151 so any mobo that support lga 1151 is fine.
You are getting a unlocked cpu so you plan to overclock right? then a z170 motherboard is perfect with your cpu it supports overclocking the unlocked processor. but if you will not buy a unlocked processor then a z170 motherboard is just a waste of money instead buy a h170/b150 and buy a better gpu.