RE: GP minnow/OS91 surpass..what prop
Erik, get three APC props - the 13 x 8 (10K rpm), 13 x 9 (about 9500 rpm) and the 13 x 10 (9300 rpm) and try them all. Quoted RPM figures are the static readings I've got with that engine and they will all unload in the air to a degree, especially the finer pitched of the three.
The Minnow is reasonably slick but has quite a large fuselage. I have an aircraft with a similar airspeed envelope to your minnow, also running the OS .91 Surpass, and for me, after much experimenting, the APC 13 x 10 was the best prop (176 km/h in level flight).