Don't any one forget that many off the shelf fuels are sold with the least amount of oil that the mfg thinks will do the job for the average flyer. If you want to experiment with smaller props and more rpm, be sure to use at least 20% oil. With ample oil, moderate load prop and a good needle setting the engine will run amazingly cool for ya.
For beginners wanting to try 8 or 9 inch props on a .40-.46 engine, you will need to try it with planes smaller than your typical .40 sized trainers to see positive results.