Re: new 120% genoa
Leech curl is not a function of the sail material but rather the amount of leech cord tension that is left on. Sails with large roaches tend to flutter when not completely trimmed in. Far too often, the trimmer will use the leech cord rather than trim this out. Far worse is leaving the tension on at all times. This eventually warps the leach leaving a permanent cup. The other big cause is motoring with the main up and fluttering. This stretches out the leach area, requiring more leech tension and more cupping. If you experience flutter on a brand new sail, take your sail maker out so he can make proper re-cut on the sail. Laminates are no more prone to leech cupping than ones made of Dacron.
Genoa size (and overlap) is really dependant upon your local conditions. In San Francisco PHRF, there is a slight (3 second) break between a 120 and 121% Genoa. Samller headsails give you the ability to point higher but with the penalty of being less powerful on a reach or a run.