There is something unstable and duplicitous about responding to one's own thread question. That said.....:

Here are some observations Paul -

1. From the standpoint of pure consumerism few of us have the knowledge / experience to articulate (meaningfully) to our sailmaker precisely what we want our new sail to do ( no surprise here , reference the "How Is Lift Created" thread before attempting rebuttal ).
2. Even the sailors who win consistently in their class are ,( for the most part), "unconscious competents" who will confidently share equal volumes of excellent and totally wrong information about why they win.
3. The classes of cat. that are approaching the refind potential of their boat.( ex: Tornado , Acat), are those classes that have attracted the most theoretically sophisticated sailors with long histories of data driven adjustments via meaningful cross testing.The rest of us have been the recipiants of these developments.
4. The practical value of "theory" in sail design / evolution, is painfully subordinate to practical and on the water testing (again, reference the "How Lift Is Created" thread).In theory a square big head main should be slower than a 1/2 parabola big head. So, why are all the big head mains square (on the water testing i'll bet ) ?
5. Because we know so little about why sails are fast or slow, we're collectively losing mountains of practical data that could advance the art generally.

CODA :

when I ended my research (alot and i'm not that stupid) and sat down to order my mainsail I included my credit card number and one specific design parameter : " Make the sail fast to "A" mark"...

We should know more than we do...

PK