Gerr is excellent but his info is dated. Four was rare and 5 bladed technology was not available in small (our size) props when his book was written. If money is no object talk to the prop manufacturers. you should be able to improve both mid-range and top speed with increased efficiency (MPG) at all speeds (i know not possible but, in fact, it is being done all of the time) with modern props. Drawback is they are expensive so the payback is protracted.