besically your props for a 47 sized engines are
9x8, 10x7, 11x6 (or 11x5 depending on engine) and 12x4 (or 12.25x3.75 apc prop)
in general for every inch in diameter you add to the prop, you take two away from the pitch

the 9x8 is the fastest prop. the 12.25x3.75 prop will have the most torque.
fastest prop= fastest model. however, to make this simple, if you put a 7x12 (following the above rule) you may have to much speed and not enough torque to fly the model (like starting your car in 5th gear)
but with speed comesless vertical.
the more torque you have the more vertical you will have. but the lower your model will fly

basically for a trainer you will have two props, 10x7 or 11x5 (or 11x6 if your engine can handle it)


as for that load factor where 10x6 = a 60 load factor. that doesnt really work

example. 12.25x3.75 = 46
and 12x4 = 48
if your theory was correct my engine could swing a 15x4 prop at the same rpm as a 10x6 because they both have a 60 load factor.
a 47 engine has no hope of swinging a 15x4</p>