i have a i5 6600k and an asus z170-e mb. i was able to get 4.5ghz at 1.350 voltage. i think that's a decent place to start. but all chips are unique, you may have more success than me.
change your multiplyer to 45x and change to manual voltage 1.350. edit: also change LLC to 5, and turn off speed step and c-states if they're on. if, after stress testing, it's stable, try to reduce the voltage 0.010 at a time. or increase if you have to.
i'd avoid going to 1.400 voltage. it'll depend on how high your temps get too. if it's unstable or too hot try 44x and less voltage.
currently i have mine at 42x and 1.200 voltage. for 24/7 use