John, Is that Carl Dodge's FAI Controline Speed plane? Here is what to remember in this debate. If someone was fortunate enough to have the best 2 blade prop for a given application, and someone else had the best 3 blade prop for the same identical application, the 2 blade will always out perform the 3 blade. Often times we have to compromise on the choice of the number of blades. In full scale aviation more blades were added to absorb the energy from more powerful engines, or as mentioned, for ground clearance. Today multi-blade props are sometimes chosen for noise reduction on both full scale, and model airplanes.
People who argue that their model performs better with a 3 blade prop, just never found the best 2 blade prop, or there wasn't a noticeable difference in performance. The single blade prop is the most efficient, but has it's drawbacks. In full scale aviation they put huge side loads on the shaft and bearings. This is punishment that the engine was never designed for. Our model engines are built to survive most crashes, so they are very robust, and can withstand side loads. Well some of them anyway! Multi-bladed props distribute the loads on the shaft, but this is way more information then was originally sought! The best advice is ask questions, and then experiment. Choose a 3 blade that allows the engine to turn the RPM's for it's best power range, and see if you are satisfied with it.