There are all sorts of rumors that Apple will release one last Intel Mac Pro. However, even in a desktop and workstation heat and power efficiency of individual cores still matter as they dictate how many cores and what frequency they can be run at. You'll notice that for both Intel and AMD the base clocks are far, far lower the higher the core count. The M1 won't need to do this because each core is only using about 5-6W. This also makes it easier to calculate what the MT scores of a Max Duo (20-thread) will be and the ST benchmarks will be identical to what we have now. Basically double everything and shave a touch off for interconnect between the dies. First order approximation of course, but this would make for a very powerful desktop. In most applications that will be faster than a 24-thread ADL CPU and quieter to boot.
For a workstation, 40-thread class chip, were it to be based on M1 which is unclear at this point as there are competing rumors, again pretty easy to estimate its performance. Because each core draws so little heat - basically quadruple the benchmark scores and shave a bit off. While granted efficiency is even more important in a mobile or physically thermally constrained environment ... put enough cores into an x86 chip and you are still going to be thermally constrained. 
