Wow!! RCKen has a point here.

Noise does not equate to power! Jeech!! I say that because this engine will perform very well and more than you ever expected it to if you work with it. Set it so the RPM are no more than 11 - 12 K and that even sounds high. It has so much power at 10 - 11 K that properly set up, it will do more than you ever expected it to.

I have an OS 75 AX on a Goldberg Protege as well as a Goldberg Skylark 70. The Protege, a high wing aerobatic trainer, has so much power with a 13.5 x 8 Bolly prop that I almost cried when I broke that prop in a crappy landing (my fault). The Skylark 70 has a 14-6 and flys like it was on rails and does absolutely everything I expected it to do, and then some.

As Ken said, don't get to concerned about the spec RPM and power levels at that RPM. Prop it so that it runs well, and in that case, I would not exceed 11K or so RPM because, as I said, it will make lots of noise, but won't be doing what it was designed to do. Prop it up a tad and check it's performance.

Over time, I have collected a box filled with props. When I get to the point where I feel that I should expect more, I swap props. This will go on for several short flights until I get back to the prop that I selected in the first place, and that was one that did not get overly agressive in the RPM range, but was quiet, and powerful.

Head on over to your LHS (Local Hobby Shop) and pick up several props of different sizes, and work on it. Swap, fly, land. Swap, fly, land. Swap, fly, land. Sooner or later you will find one that works great and I would be willing to bet that the one you select produces adequate (if not more) power, at a lower RPM, and make quite a bit less noise.

CGr.;