I only race the TT 40 PRO in 424 which we only get to use the APC 9x6 prop, but here is some general information. If the plane is heavier than 3.75 lbs and draggier than a quickie, I would be looking at 9.5~10 inch diameter props that I could spin at or slightly over 16,500. You either get more diameter (thrust) or pitch (speed). If you look at AMA racing classes, you will notice the cleaner the airframe, the smaller the diameter and higher pitch props are used. You have to decide if you can fly smoother and carry more pitch, or if you yank it around the poles hard and need more diameter. As a rough rule of thumb, if you add 1" of diameter, you must subtract 1" in pitch to maintain the same RPM. The formula works both ways if you are using the same manufacturers props.

No matter which prop you end up using, there are a lot of basics to racing you should be conscious of. I have posted a document I put together a couple of years ago for a racing clinic I did here in Florida. There is quite a bit of information in it I think you may be able to adapt to your form of racing. I put a section on engine set-up, break-in and lots of other goodies to help out the new guys. Take a look at it and see if it helps any.

Good luck and I hope you enjoy racing as much as I have!