RE: 4 stroke vs 2 stroke in carrying up jumpers
It depends on the plane. I prefer electric but that gets real expensive when the plane gets big. The reason why I prefer electric is that it is cleaner, if you use nitro oreven gas you have to worry about the divers getting soaked with oil from the exhaust.
I use the Sr Telemaster with a worn out (but it was cheeep) OS 91 FX but I only haul one as of now (3lbs). I did however run the exhaust tube to back of the plane under the elevator to keep the diver clean and this works well with now effect to the engine other than a cool sound.
Two or Four....I rather two for weight issues but there or some people that say Four for the extra torque.....I know I didn't answer your question but I think its your preference, it really doesn't matter. I would overpower the plane though just for insurance.