Maybe a little overstated, but trying to come up with common equipment for aerobatics and pylon racing is like purchasing an Indy car to take the family on vacation.

I cannot help you much with the aerobatic part of your question. The prop your are using sounds about right.

For Pylon Racing on a good quality 40 engine (Not a racing engine) I would start with an APC 8 1/2 x7 prop. Any more pitch than that might be a bit heavy. 6 1/2 or even 6 pitch might be better, depending on the power of the engine.

Running props on the ground and reading RPM has only limited value for pylon props. In the end you will have to try it and fly it to get valid results.

Ed S