If at all possible, Stay Away From Gearboxes and use a direct drive brushless motor on Everything, except giant size Planes
A 400 size motor will work Great with your plane with the 41" Wing span, Hope that helps, Chellie
And if you're after maximum thrust and a long flight time, the GWS EP9050 prop and a 11.1v 1500 30C Lipo battery will give you excellent results.
Dont Worry about Watts when Starting out, use oz of Thrust, its much much Easier, the 9x5 prop and a 1500mah 3 cell lipo will give you about 30 oz of thrust, more than enough for your plane.
Battery Size ***** Propeller Size ********* Thrust (oz.)
3-cell 11.1v, ***** GWS 9050
Prop,******** 30 oz.
of thrust **** @ 15 amps