Hi Tim,
As usual, a great photo of Gary styling on an awesome boat.
I think that he looks pretty much sheeted in max there, looking at the blocks. Most cat mainsails are designed with a certain amount of twist built into them, so if your leech stands up all the way to the top, you are in effect oversheeting the bottom 2/3 of the sail. I`m certainly no expert here, but from what I understand, twist is good, not only to depower the sail, but aerodynamically as well. Something about the wind higher up flowing faster than lower down, or at a different direction, whatever. Maybe the aeronautical engineer`s who visit these forums can explain it.
Looking at modern windsurfer rigs, the sail is designed to have quite a lot of twist, so much so that when you look at the sail on the beach, the leech is floppy, this depowers the rig before you have even sheeted in, but also has the effect of creating a large amount of twist. Now why would they do that if they could rather rig a smaller sail and have the leech stand up straight, it would still depower in the gusts due to the flexible mast. The answer must be that a large sail with a twisted off head is faster than a smaller sail with a straight leech. Perhaps in cat-sailing this is all different, maybe too much twist will hurt your pointing ability, but if your speed is much better you might still be first to the weather mark.
Just my opinion, so all those who have a degree in aircraft or sail design, feel free to straighten me out.