Peter,
Sorry for the delay.
I carried out some tests on my WM14 to see how hot the motor would run at maximum speed. I'm not sure what value this will be to you as I wasn't actually cutting metal and the motor cover was removed, but you may be able to draw some conclusions.
Start – switched to high speed range and turned the speed control clockwise until it would turn no further. The speed indicator showed 2235 rpm.
After 5 minutes – the motor was only very only barely warm to the touch. Speed had increased to 2271.
After 10 minutes – the motor was still just slightly warm to the touch. Speed had increased to 2301.
After 15 minutes – the motor was pleasantly warm to the touch. Speed now 2319.
After 25 minutes – the motor is warmer, but I could easily bare the back of my hand on the brush end (warmest part) of the motor. Speed now 2355
I ended the test here. There were no nasty smells and I did not get the impression that things were overheating. It seems curious that the speed increased quite the way it did.
I hope this is of some help.
Regards
Geoff.