I have several of these engines they have loads of torque something in the 15/4 to 15/6 is going to give you good performance while not bogging the engine down,you can go with a 16" prop but in the 4 pitch range for 3D, on scale planes a 14/6-14/8 works well I have used 14" props with 3 blades up to a 10 pitch but they seem to bog the engine a little and I couldn't get much more than high 8,000's.

top RPM expectations are around 10,000 usually I spin it up to 10,300 and then roll the needle back to about 9,800 and they run like a sewing machine, it all depends on the prop your using as to what your max RPM is whatever you get in that range then back it off about 300-500RPM and it will run well and not over heat.