> You know, I'm something of a CPU engineer myself :D

Actually almost everything what you wrote is not true, and commenter above already sent you some links.

7800X3D is the GOAT, very power efficient and cool.

The only reason the 7800x3d is power efficient is because it simply can't use much power, and so it runs at a better spot of the efficiency curve. Most of the CPUs won't use more than ~88w without doing manual overclocking (not pbo). Compare that to e.g. a 7600x that's 2 cores fewer on the same architecture and will happily pull over 130w.

And even if could push it higher, they run very hot compared to other CPUs at the same power usage as a combination of AMD's very thick IHS, the compute chiplets being small/power dense and 7000 series X3D cache being on top of the compute chiplet unlike 9000 series that has it on the bottom.

The 9800x3d limited in the same way will be both mildly more power efficient from faster cores and run cooler because of the cache location. The only reason it's hotter is that it's allowed to use significantly more power, usually up to 150w stock, for which you'd have to remove the IHS on the 7800X3D if you didn't want to see magic smoke