RE: 4 stroke, for speed planes?
As already stated, you go with a smaller higher pitched prop to take advantage of the lower RPM torque and power curve on a four stroke engine.
Besides YS, there were some rather exotic overhead cam engines that might work too. I don't know if they make them anymore though.
But there are a lot of factors involved. Different planes may need a different prop, One plane might use a 12 inch pitch prop but another plane works with a 10 inch pitch prop. You have to keep the max RPMs under the max rpm limit for the engine still.