That's why it's best to buy from somewhere that lists the RPM at the nominal voltage (MFA does this) which allows you to match it to the maximum RPM of a particular size propeller (Raboesch used to have this info somewhere).
A prop - motor chart would be great if such a thing exists. However in the absence of something like that us poor saps are blundering around in the dark. The general concensus of opinion seems to be that a 540/1 is not suitable with a 50mm prop. A 50mm prop looks right for scale I am building in I think.
However there is then the 'guide' from a certain retailer saying that a 540/1 is as follows. I read this as saying that it would be suitable. What do I believe.
"RE 540 3 - 9v 7.1A 10,800 Rpm @ 6v £ 6.95 A larger sized motor, also known as Speed 600 An industry standard general purpose high powered, high rev. motor for Electric Flight & Fun Fast Electric Boat Racing.
RE 540/1 4 - 15v 3A 13,360 Rpm @ 12v A larger sized motor same Dia casing as the 540 but wound for low drain and high torque,
suitable for medium scale model operation replaces the old 545 motor which is no longer available"