You're saying that a spinner had a lower rpm than a prop nut? That doesn't make sense to me, except maybe as a vibration thing, though I certainly don't know enough to be sure about that. My guess would have been that a spinner would have higher RPM than a prop nut, as the spinner covers the hub of the prop and smooths out the airflow in that area. But I am totally guessing about that. Hmm, now that I think about it, maybe it's a rotational inertia issue? A spinner has more mass farther from the center of rotation than a prop nut? I'm still guessing though.

One thing I do know from first hand experience is that a spinner can give you a higher level airspeed compared to a prop nut, depending on the airframe and the size of the spinner. But I had never heard of an RPM difference between the two.

Shaving off the mold flashing on the prop makes perfect sense to me, though I had never thought about it before. I assume the airflow over the blades is smoother, creating less turbulance, and therefore less drag on the prop blade, which results in higher RPM. I do shave my MAS props to keep from getting cut and to reduce damage to anything I might hit, but I never considered it a performance thing. Interesting.