Interesting chart, but the top end range of the sails, particularly for the intermediate and amateur sailors is very high and frankly, WAY OVER reasonable limits for an 80kg sailor. A 5.8 sail with a top end of 35 knots for an amateur? 41 knots for a 5.0? I don't think so!
The Neil Pryde amateur sailors must all be PWA members racing the slalom circuit. They are over selling the range of their sails. I suppose the top end numbers could be true if you consider a few select speed sailing sites around the world with very flat water and very small boards, but even an 80kg amateur speed sailor would have a handful with a 5.0 in 41 knots of wind, and an intermediate with a 5.0 in 47 knots. Give me a break!