One of the first model aviation guide books I ever cracked open claimed that some C/L speed plane combos acheived 100% prop efficiency, if not better.

No doubt that weight = power in a dive. A heavy enough plane can push its' engine well beyond any rpm that it could reach on its' own. Reminds me of the time I landed [a very tail heavy] plane after a nice power dive, with just a short stub of connecting rod hanging out of a ripped open crankcase.

It was a G-21 SuperTigre .35