We managed to push the Core i7-8700K a little further to 5.2GHz, but it requires a much higher voltage of up to 1.532V to maintain its stability. Feeding the CPU with 1.532V will of course result in a much higher temperature, ours topped at 94°C within seconds and thermal throttle starts kicking in.
We backed a little to 5.1GHz, with 1.365V supplied to the CPU and the result is just as good. The CPU temperature after we lowered the CPU frequency to 5.1GHz hovers around 83-84°C, which isn’t bad at all. The only issue we have is the temperature of the MOSFET that skyrocketed to 80°C when we started our stress test at 5GHz.