it does not work exactly like that,, the longer bow will be more forgiving as you learn, if you make a mistake it will more than likely still make a bow,,,I could write a chapter on it,, the longer bow will shoot great if tillered right,, there is not an exact length for any draw,,,it depends on the tiller design etc,,,,, as they go shorter, it takes more skill with very little gained in performance,, your figures you are quoting are not what most go by anyway,, 64 for 26,,, 65 for 27,,, 66 for 28 ,,, is a good staring point,, as you gain experience you can go shorter,,, if you make the longer bow and miss the weight,,, the longer bow can be cut shorter and tillered so you hit your weight etc etc etc,,,also you have nothing to loose by making the longer bow,, if you do want to shoot the bow at a longer draw guess what ,, the longer bow will accommodate ,, the shorter bows are more limited in how far they can be drawn etc, etc etc etc etc,,