The problem with this kind of comparison, is that you can't change just the number of blades and nothing else to get a realistic result.
In reality the differences will be due to variations in blade length, aerofoil, control of the pitch management, and, interaction with the airframe/engine/spinner combination, to name just a few.
The only way to make a real comparison, is to fit the new prop, and carry out objective, back to back tests, under the same conditions.
As someone said earler, if you're going to get the 3 blader for free, and you can keep the old one, you have very little to loose.
MJ
