The second part of you question makes assumptions about 'more' and 'less' thrust. Be careful. The faster the model is flying the greater the thrust from the engine/propellor. Thrust, when the model is flying steady state, straight and level, is equal to drag. The faster the model is flying, the greater the drag, and the greater the thrust. So, in your case, the smaller, high pitch, higher revving prop is creating more thrust. It is that simple. What you are alluding to is how efficiently that thrust is created. And that is entirely dependant on what you want the model to do. Put very simply, if you have a high drag model, that can't fly very fast anyway, there is little point using a 'high speed' engine/prop combination, and vice-versa. And as always, the best prop will only be found by experimentation (fly the thing) and likely won't be the prop you thought would be best.