Comment by DoctorOetker

I am the person who gave the pyramid shape as a didactic example (convexity means we can ignore self obscuration, and giving up 2 of the 4 triangular side surfaces of the pyramid allows me to ignore the presence of lukewarm earth).

My example is optimized not for minimal radiator surface area, but for minimal mathematical and physical knowledge required to understand feasibility.

Your numbers are different because you chose 82 C (355 K) instead of my 26 C (300 K).

Near normal operating temperatures hardware lifetime roughly doubles for every 10 deg C/K decrease in temperature (this does not hold indefinitely of course).

You still need to move the heat from the GPU to the radiator so my example of 26 deg C at the radiator just leaves a lot of room against criticism ;)