It determines speed more than power, but in the long run both are affected. When you are first learning to operate the unit, it helps to keep RPMs low and operate one function at a time. It keeps the machine from performing "jerky" and wearing out the joints. As you improve your feel of the controls and want to start operating more than one function at a time, more RPMs will be required. The "feel of the controls" I'm talking about is your ability to feel the flow through the control and feather the actions of the unit smoothly. Smooth controls are the true key to speedy digging.
I'd start at 1300-1500 RPM. Once skilled and using two or three functions at a time, 2200-2400 would be the high end.
