RE: 4-Balde props, pros and cons?
You are putting words in my mouth, I did not say many of the things you claim.
The argument was that full scale goes to multi-blade props for ground clearance. While this is sometimes true, it is usually in an effort to go faster, especially at altitude. That is why many small GA planes go to three blade props and why many racers go to them as well.
The delta V of the props is related to thrust. If you put a very course prop on a plane the delta V will be very close to 0 at the max speed, that is because the speed is limited by the prop and any delta V will be equivalent to the drag of the airplane. Thrust is equal to delta V time area. Put a smaller diameter prop on the plane and Delta V speed will be higher at the max speed of the former prop, and thrust will be higher at that speed despite the smaller area. That is true because thrust is always equal to the drag + acceleration.