More than happy to learn something through a mistake in my calculations !

Regarding the 50%, I assumed that they stated this number because this is when the battery is in bulk charge and can suck up as much as you can give it.

For the 250W, I hadn't even seen that, good catch. Maybe 250W is the peak power that cannot be sustained for thermal or current rating reasons ? 250W for a 12.8V 10Ah battery is 2C, so that should not be the limiting factor. I do not know about the motor or the ESC

Also, for sure the maximum range is not achieved with the top speed !