Okay, so you have a Z-series MoBo that does support OC.
i7-6700K OC depends on how good chip you get. With average chip you should be stable on 4.6 Ghz. If you're lucky with good chip, you can even get 4.8 Ghz out of it. If unlucky, your CPU would be stable on 4.4 Ghz.
Also, here's a guide to read: http://www.overclock.net/t/1570313/skylake-overclocking-guide-with-statistics#