I am not sure about this but there seems to me to be several different factors -

So efficiency to me starts with the last of these, and works back up the list.

As an example, a propellor for a rubber powered model has low power input and is required to transmit that power very efficiently to move the model. So these props are broad bladed, fairly high pitch, and move a large amount of air quite slowly.

In recent times, there has been a move toward high aspect ratio props particularly for F1B/Wakefield. Prop d/p's of 24x22 are not uncommon. There are photos in a recent magazine of a Russian who is using a 28-26x26-22 variable diameter/variable pitch prop. The blades on these are all narrow at 25-30mm wide at 40-50% halfspan. What has to be remembered is that these props are all driven by comparatively short, high powered motors in a composite tube. Put one into a traditional stick model and the two ends would meet in the middle at half wind.

Move up to the sport diesel power ff/rc assist model and the props are all very similar. Blades are now about 1/2 to 3/4 inches wide, with some taper, and all are turning at about 7k to 12k. And they will move a model along at a suitable pace.

Put the same prop on a Dooling 61 or one of the modern speed or combat glow motors and it would destroy itself and the motor.