To determine changes in engine would be to use a tach. That may work out easier. Whatever combo allows the prop to spin faster would be an indication the upgrade was going in right direction. I swapped out carbs before in engines and noticed an increase in rpms after the tach was put on it.

Or you can do what i did with a car before. As crazy as it sounds those mobile police radar trailers things you see on side of road work. I drove my car against it and it picked up the cars speed. It was pretty consistent also. That would work out good if you happen to see one. Then try out the different parts.