EDF sizing
 

Looking at getting into EDF's, I'm wanting to put one on a scratch built foamy delta wing and a Stryker. I'm trying to work out what size fan/motor wattage/RPM to use, is the Watts/lb formula for prop driven planes applicable to EDF's, I've heard EDF's aren't as efficient as prop driven? With propped planes you can work out approx speed from prop pitch speed, can you do that with EDF's?
Thanks
Charles