Also,i find this interesting:
"Usually we bench at 1,8-1,95 Volt on LN2 and on Load I'm pretty sure the CPU core will also hit positive temperatures very fast. Replacing the TIM we could lower the temperature by about 10 Kelvin but often the maximum clock was lower in the end. Unfortunately I have no explanation for this."
When pot is at negative temperatures,there is no way cpu core is at positive temperature,ihs should be one of the best things for isolation in this case
Best way to measure die temperature would be to sneak a probe under ihs near the die,core temp or real temp or whatever are not reliable under zero....