How to overclock my 6700k, and how far?

Aurum9

Commendable
Jun 6, 2016
14
0
1,510
I have an i7-6700k that I wish to overclock to get some extra performance. However, I'm not sure how exactly to do it. I just have a few questions.
-First of all, my mobo is an Asus Maximus VIII Hero. In the bios, I can set the core speed and the voltage using a manual mode, however, my voltage is always significantly above the set level at full load. Why is this? Should I let my motherboard automatically set the voltage or will it set it higher than it needs to?
-Also, how far should I push my temps? I have a Cryorig H7 (cheapish air cooler but gets the job done). I heard that 90 is a safe limit.
-Similar to above, how far should I push my voltage? How can I ensure that my voltage doesn't exceed the level I set in my bios?
A guide or something of the sort would be very useful...any help is appreciated. Thanks!