In boats around 30'' or less in length, and in winds of average strength, I don''t think the type of sail material significantly affects boat speed. You can compensate for the stretchiness of dacron sails by sail trimming techniques. In very light or very strong winds, I think laminated sails have a more significant advantage. In light air, the reduced weight aloft enables a boat with laminated sails to continue ghosting and maneuvering after dacron sails have collapsed. In heavy winds, it becomes increasingly difficult to trim the stretchiness out of dacron sails. Logically, I suspect the difference in the sail materials becomes much more significant as the size of the boat and sails increases.