I totally understand the concept of, "Friendly" competition. It will still depend on which engine in the .90-.91 size that you are considering. If it is something like a Webra .91 Speed, then you will need to run a different prop than say, an OS .91. You need to choose a prop that will take advantage of the engine's max RPM and torque numbers. A slower revving engine can make better use of a prop with tons of pitch, while an engine that makes more RPM with a lower torque number can really spin a prop with a little less pitch and still makes more thrust. The answer is still the same....It depends.

Bill, AMA 4720
WACO Brotherhood #1