OK, I just learned something. My old 2700x was probably not the problem, and was probably fine. The new chip did the same thing. Even on a 240 rad watercooling it was 1.35 vcore and 3.9 ghz@75c. So just for fun, I set the bios to1.2 vcore and 4 ghz. 65c and working@100% for an hour. It just never occurred to me that the Taichi motherboard would overvolt ! I will keep playing now that I know the bios is flawed.
The problem is not so much the cooling capacity of the radiator, the coldplate/pump isn't able to quicklt transfer heat away the cpu itself. My rad is still cool(nowhere close to heatsoak) and you can feel that the inlet is warm compared to the exhaust.
I have only let Prime95 and OCCT run for about an hour and a half as I am not comfortable with those temps. I have lowered the max temp limit so that very heavy loads will let the cpu clock down and keep temps around 75C. Games aren't that stressful so they will let the cpu sit pretty at 4,3~4,35GHz even with the lower temp limit.