(NVIDIA) Fan-Based-Heatsink Designs are probably wrong. (suck, don't blow ! heatfins direction)

Convective and radiative cooling only. And not much of the latter if the thing is made of shiny metal. Proportional to flow plus a small additive constant isn't exactly rocket science. In any forced air cooling design worth its salt airflow cooling totally dominates.

PWM to vary the power provided to the fan so the work done by the fan is on moving the air through it and to first order the output velocity field scales fairly well apart from deep inside the heatsink where there is or should be some turbulence.

It occurs to me in this discussion that the performance of a standard rectangular vaned heatsink might be improved by putting diagonal wires through the vanes at say 45 degrees to generate vortex wakes that mix up the laminar flow after the first or second set of vanes.

Measuring rpm of the fan against power supplied will give you a decent proxy for back pressure and many PC fans are so equipped.

Perhaps but I would guess only by coincidence since the main output drive buffers are probably physically close to the edge of the die.

Regards, Martin Brown