Not sure if this i the proper place for this , but I'm gonna give it a shot.
I am finishing building a Multiplex Magister w/brushless outrunner. Hobby Lobby sells an outrunner kit, but I already had an E-Flight Power 25 outrunner,, so I decided to use it. I'm running a 45 amp ESC and 11.1V 4000ma lipo......Hobby Lobby specs a 12X6 prop for their conversion, but the AXI motor they use has a higher KV rating. I installed the 12X6, but it really looks tiny. E-Flight says that the motor is good to a 14X7. I'm actually thinking this may be a good size for my set up.....There's plenty of room for the 14, but I'm not sure the motor can swing it.....How the heck do you select the proper prop, without buying half a dozen to experiment with???......Pat

Also.....I found that the slow flyer props will pull more watts, for the same pitch and diameter, but a slow flyer will not fit on the prop adaptor. It requires a thin electric. So with a thin electric, I'm thinking the 14 inch would be ok as the tips are very narrow....VS. the wide paddles of a slow flyer.....