with i7 6700 you can not overclock only the cpus with a k at the end of the number can be over clocked sorry for the bad news on the cpu
with overclocking your enemy is heat the more you OC the GPU higher the temps
there i always risk in Over clocking
if you want to play around with it download MSI afterburner pretty easy program self explanitory
i have dual gygabite gtx 970 g1 OC editions both of them are OC to +144 core and +500 memory at 68c thats a stable OC
use the above settings as your base if the temps go over 70c stop the OC