I've been trying to overclock the i7-6700K on my Z170 Classified K using a liquid cooling setup (quad radiator; loop shared with two Nvidia 1070's). It seems that no matter what overclocking and/or voltage settings I use, Prime95 tests always eventually fail, usually within an hour.
I've now set all the CPU settings in the BIOS back to defaults--stock speed (4.0GHz) with Auto voltage. Even configured like that, Prime95 fails.
At idle, the CPU runs just under 30°C (ambient temperature 23°C). This seems a little high to me, but considering the loop also cools two 1070's, it's understandable. When I run Prime95 with its default settings, the CPU runs between 50°C and 60°C, with occasional spikes up into the 70°C range. This is well within tolerance, but still seems a bit high to me.
The thing is, I'm not sure if my problem is a bad CPU, a bad cooling block, bad or mis-distributed thermal paste, or some combination thereof. Does anyone have any suggestions of how to narrow down the problem?