RE: Propeller Worms
There are two thick branches on this tree...
A more efficient prop may have a higher load, because it transforms more of the engine's power into actual pulling power (thrust).
A less efficient prop may have a higher load, because it transforms more of the engine's power into turbulence...
The prop factor is supposed to represent the relative load of the prop, compared to other props of identical pitch and diameter.
...Not its efficiency...
The load could either increase, or decrease, from both higher efficiency and lower efficiency...
And as to the APC 11x6 prop... There has been a unanimous opinion on these pages that this specific prop exerts a MUCH higher load on any engine, than its prop factor suggests. It 'gulps' up more power, but gives good performance...
I suggest Pé Reivers look closely into this specific size... It may warrant a prop factor of its own.
Maybe categorizing only by brand and type is insufficient.
I found the Master Airscrew K Series props; although black, probably need a higher prop factor also.
They are spun more slowly than APC props of the same sizes.