It is not just a sail question, it is also about having the right mast for the sail. If you already have average bend curve masts SDM masts that fit Severne sails then the ultimate powerhouse is the Severne Glide 8.5.
According to the German Surf magazine it indeed has the power of a 9.5 but in a lighter package. The other tractor sails could not compete in the low end. I think they claimed they were able to get it going in 9 knots. But it of course overpowers relatively early as well, not recommended for gusty locations.
Pryde on the other hand requires a flextop mast to work properly, and you probbaly don't have any of those :-)