135% vs 150%
For a head sail that is left mounted all season and especially one that is flown (and partly furled) in light to the upper range of moderate conditions, you can consider a radial design that is constructed with heavier cloth at the leech and lighter weight material at the luff. This is definitely a ''compromise'' but may serve you well through your expected conditions. With the sail fully exposed/unfurled during ''light'' conditions the lighter weight forward sections will take better shape albiet the aft heavier sections will need to be shaped correctly. When partly furled, the after section will be better able to stand the strain of the increased force of the wind; and, the lighter weight forward section will furl tighter and more compactly on the foil resulting in a ''fairly decent'' shape (but not perfect). Most furling headsails can only be reduced by about 25-30% and still have relatively good shape. As regards a foam luff, it is possible to get a reasonably good furled shape -- without adding a foam luff, it all depends on the knowledge and expertise of the sailmaker; he/she will also offer ''foil attachment tricks'' to affect good shape (for a sail without a foam luff) when partly furled. The disadvantage of a foam luff is that when furled you will have a very large cross section of the rolled material which greatly reduces the air flow efficiency across the sail. I''d sit down and discuss in detail with a reknown ''local'' sailmaker such possibilities if you''re looking for a ''one size fits all sail". Obviously such a sail cant be obtained from a mail order house that constructs their sails offshore. Such a sail will need precise backstay tension and forestay sag limitations. If your intentions are simply cruising with occasional club racing, etc. take a good hard look at some of the newer "cruisiing laminate" sail materials.
For areas that are reknown for long periods of ''light'' winds a good addition to your inventory is a free luff ''drifter'' that is flown free and not attached to a foil (so that you dont have to dismount the furled headsail). These are made from extremely light material, so the relative costs will be lower in comparison to a full/''normal'' headsail. Since these light materials are relatively easy to sew together, you can opt to construct one yourself from a ''kit'' if you have access to a ''decent'' home (or better) sewing machine - www.sailrite.com