Thrust vs. Prop Pitch

[Madfish]

Lower RPM also means highest torque. Just because the engine spins fast doesn't mean it has the power to pull through load. In other words: once that initial inertia is gone the engine suffocates.

It's like with a car - most of them have the highest torque around 2400-3400RPM - beyond that you might have a spike but only for a brief moment and after that the engine loses power rapidly.