I don''t have all the answers, but will start with what I think I know, and others can chime in.
The most reliable opinions I have heard say that the laminated sails are greatly improved, but still are not as durable as dacron. I race my 20+ year old dacron sails against boats of the same and different designs that use laminated sails, and beat them routinely. However, in light air the laminated sails have a big advantage, because they are much lighter in weight than dacron and they will fill and take their shape in less wind. If you are involved in local club racing, dacron sails will serve you well. If you buy laminated sails with the thought that they will move you up from the middle of the pack to the front of the pack, you will be disappointed. They don''t help that much. If you are into racing at a more competitive level, you should have laminated sails, because you can''t afford to concede the light air races to them.
In my opinion, the bigger the boat, the more important it is to have laminated sails. In smaller boats (less than 30") you can compensate for the stretchiness of dacron by constant sail trim. In larger boats, the resistance of laminated sails to stretch is more useful.
My old sails were built by North, and are excellent, but last year I replaced the mainsail with a plain vanilla brand mainsail, and it is every bit as fast. North used excellent dacron sailcloth 20+ years ago, but my guess is that modern dacron sailcloth is at least as good as 20 year old North fabric. Time will tell how durable they are.
On both my old North and my new plain vanilla mainsail, I had them built with a racing shelf foot and flattening reef, and highly recommend those options. The shelf foot creates a very deep pocket in the foot of the mainsail, which provides more power in light air, and the flattening reef allows you to eliminate the deep pocket and flatten the foot of the sail very quickly and easily when the wind pipes up. They are not expensive options when you order a new sail, and they are very useful, both for racing and cruising.