Not particularly basroil, although OP you should definitely look into what overclocking entails and watch a fair few videos/guides before attempting it.
You can expect to hit a stable 4.5GHz almost guaranteed with a 6700k, a 4.7GHz overclock is what I find to be the sweet spot, although not everyone can achieve this.
It is best done by gradually increasing the clock speeds, and then the voltage when you start to notice instability. Repeat this until you reach your desired OC.
If increasing the voltage isn't resulting in a stable OC within reasonable boundaries at say 4.7GHz, then back off to your last stable result and leave it, that's the best I can describe it.