Update on the brompton:
With my little conhismotor mini hub at 4.6 kg, I do peak at 2500W and he handle it without breaking a sweat. But I only use that much power for acceleration and I don't cycle very fast (17-23 mph).
I'm actually running slower than my actual "limited power" bike. Most cyclist are faster than me but I'm more careful about security than going faster than them.. And I know I'm way faster
I believe with great power comes great responsibility
However, my mini direct drive motor is really really power hungry. I only cycle around 17-23mph but I'm using around 18wh/km. That's huge.
At 500W continuous I'm around 25kph. That's not really efficient. Not sure if it's because of the high voltage, leading to the low efficiency band of the motor..