A lot of these questions can be answered by anyone that has a good basic knowledge of aero-modelling, where you can alter things quite cheaply. (i.e. props cost less than £4..)
Lets say you have a model glider that has a brushless electric motor, you can try several different props, all of which will all load the motor to exactly the same extent.
If you try a 12x4 (diameter 12 inches, pitch 4 inches) then the glider will climb vertically, but will only fly very slowly.
An 11x6 would give a 45 degree angle of climb and a moderate cruising speed.
However a 10x8 would be very poor on the climb, say just 10 degrees, but the top speed would be ballistic.
You can choose whatever suits your flying style. The VP full size prop can give you the benefits of a variable pitch but obviously cannot change it's diameter, which is needed to give the motor a similar load.