ORIGINAL: Campy
I agree with you on the flywheel effect. It can allow you to get a lower idle. However, an 11" prop (for general flying) on a 40 has a high probability of bogging the engine down. Remember, you are talking about a SIG Rascal, not a 3D plane.
I'm not convinced that an 11" prop with the right pitch would be a problem for this engine. Have you taken the opportunity to review what props OS recommends for the engine?