RE: need help picking first
Funny how that combo of a Master Airscrew 11X7 S-2 prop on a 55AX + tuned muffler works like magic on a lot of sport planes.
A gal flier, runs the 55AX with a red Jett muffler and a 11X8 S-2 cut down to 10 3/4" on a WM T-34, it's quick, some guys use an APC 10X8 or 10X9 with that set up.
There guys running APC 10X10 on there Vipers.
The Q-40 is a clean, quick plane, I don't think you'll get the most out of the 55AX on that plane unless you can swing 10" prop or find a seriously over square 9" prop.
An old FX series may do better here, or something that turns higher rpms so you can use a 9" prop or smaller.