[Graham]

Motor availability is a problem, nearly half of those on the list aren't commercially available any more, Fly, MRRC, Ninco, SRP.

What about some of the up-to-20k motors on the current Global Touring Proxy list?

I agree that it is a problem trying to get a decent range of motors from our UK supplier.

many of course would be available in the RTR cars if entrants have them to use.
Some are available on a limited basis, the Pioneer 18k rpm is still available to buy from Slot Car Union for example but rarely seen at PSR. The SRP ones are bought in a seemingly random manner. 

I have tested the Scaleauto 20k motor and its really a  22k rpm type, the NSR 20k motor is possible according to my measurements but I would need to check again.
The Slot it 21k motor would be OK to consider , but the 23k motor is probably too strong for these small  narrow cars. And there is the issue of ID of the Slot it motors, luckily recently they have introduced the black wrapper which could be an answer.