You make a difficult sport more complicated with your wind measurements!
Looking at your sail quivers, you have it covered from 7 knots (F3) to 25 knots (F6).
Wind conditions never stay constant. Even if you got the right sail when you started, you may find it either too big or too small when you are out on the water. May I suggest you try using the outhaul pulley system? It will make a big difference in your sailing. Modern sails have quite a big wind range and a good sailor must be able to adapt to changing conditions. Ben NED57 came in 2nd in Aruba using 1 board, 1 sail and 1 fin throughout the competition :-)