The other day a pilot at the local club tried a Top Flite 10X8 on his Enya 40 powered trainer. It would not even get out of it's own way!
He changed it to a 10X6 and it found it's power.
In addition , just to confuse the issue different brand or styles of prop will load the engine differently.
I think just loading up a lot of different props and trying them all will learn you a lot.
Just remember to adjust the carb for any prop changes.