Hi again Oldhorse,
Ahhhh.... I thought you might be looking for a sail for sub-planing conditions (with the centerboard down/deloyed for < 10 knots of wind.
I would look very hard for a Severne Glide 7.5 or 8.5 m2. Get the light 100% carbon mast and you will have a sail that will get you moving and keep you moving even in the lightest < 5 knot winds.
The sail is so light that pumping is easy.
I think the Glide sails were basically designed for the Serenity, and a 7.5 Glide on a Serenity is an awesome combination in < 6 knots of wind when everyone else sits or pumps their brains out.
Just a suggestion to keep you going in < 5 knots.
Do you know about "flutter pumping".
To do this you really just rythmically sort of "shake" the sail to keep the upper leech (where it's a little loose) flapping.
It's not about the arms, but more about moving your upper body in synch with the
sail so it just sort of flaps.
Flutter pumping is much more efficient and take alot less strength and stamina that normal
pumping and will get you back to the beach in absolutely zero wind.
In fact, when the wind is near zero, you can almost pick your direction and flutter pump straight back to the launch.
If there were 3 knots or more of wind, you would have to take the wind direction into consideration and might not be able to go straight back to the launch.
Give it a try. It's returned me to the beach in absolute zero wind on a formula board several times.
Hope this helps,