Weight? Performance wanted?
50 - 70 watts/lb = min for light park flyers
70 - 90 watts/lb = trainer and slow flight
90 - 110 watts/lb = sport aerobatic & fast scale
110 - 130 watts/lb = advanced aerobatic & high speed
130 - 150 watts/lb = light 3d and ducted fans
150 - 200+ watts/lb = unlimted 3D
Check out the set ups at 3DHS for the 55" and 87" (either side of your acft) planes. It might give you a too low and too high starting point.
http://www.3dhobbyshop.com/SearchRes...x?CategoryID=4