Hi Dark
With Turbo technology, A single active Core can obtain 3.6-3.8GHz however the more active Cores in use at a given time will decrease the frequency.
MAX turbo Boost for i7-8700 is 4.6GHz.
Turbo Boost makes use of headroom available however headroom available decreases as the number of active cores increase. When the number of active cores is increased, the maximum turbo boost frequency will drop. When all cores are active, the maximum turbo boost frequency for your processor is 3.8GHz.
To Overclock beyond is dependent on Manual Overclocking and higher frequencies will vary depending on your Cooling system and the sample quality of your CPU (Silicon Lottery)