You have to realize the less pitch there is the more thrust there is, simple as that. Then of course that limits your top end (hence the need for adjustable pitch on full scales) but that isn't what our 3D stuff needs anyway.

If you have a big heavy or uneffecient prop (like Zingers) then it will load the engine down more, and it will obviously not spool up as fast or have as much thrust (bad airfoil). For my large gassers I like the Fuchs props (27x10) because they have narrow blades, are very light, and have a nice effecient airfoil. All the best characteristics for 3D flight.

If you want to try different props, try and keep the ratio of diameter and pitch the same. As in a 19x4 to a 18x5 or thereabouts.