On second look & reading Ill add that the ratios listed have about a 12% spread. Thats likely to make less difference than a pitch change. All the other prop factors count but pitch being the supposed measure. I doubt changing gears would do much & prop changes are easier. 12% wont be likely to relate directly to MPH. An all out racing crew of a boat engineered to near perfection would find gear ratios more important than a guy tryin to get more performance..