I spent about 2 and a half hours out on the lake today trying out a "new" jib on my M-15.  Weather service said winds were 10 to 15 (seems to me the gusts might have been a little higher), and I used a "genoa" I had made for a Bauer 10 I used to own, which is probably pretty much a large storm jib.  Anyway, GPS said I averaged 3.9 mph withs max speed of 6.4 mph and no stress, didn't dump the main or even spill a beverage.  Great day on a great boat. Mike