I received a great suggestion from the Eurobricks forum – test the 42065 RC Tracked racer with PF Train motors. Their rotation speed is almost as high as the buggy motors, so definitely worth trying.
Here is the quick setup I created:
Based on my tests the speed is pretty ok – definitely faster than the M motors, but not as fast as the buggy motors. Unfortunately the climbing abilities are not that good, the PF train motor starts to slip quickly when it is loaded. The maximum slope it could climb was around 20 degrees only, worse than the M motor version.
The speed could be increased if I would install 2 additional PF train motors, there’s enough space for them if the power source is moved. Unfortunately I don’t have two more, but I would be happy to see that configuration if any of you have the necessary amount of motors 🙂