My records show that with the Beta 38 and a 2.5 to 1 reduction transmission the Maxprop set at 28 degrees or 16" pitch (X=D and Y=K), one boat got 6 knots at 1800 RPM.
Another owner in San Francisco set his at 26 degrees (X=V and Y=B), although I do not have any data from him regarding performance.
If you have a 2 to 1 reduction, then the prop should be set to a lower degree, such as about 20 or 22 degrees.