Pepin,

I'm kind of liking Kwiksilver's idea. Use a spin that is more like a Genoa, maybe even a little less sail area. I think the flat sail would allow you to broad reach in higher wind and or it would allow you to bring the boat up higher toward the wind than the spin does. Even if the spin holds its shape it gets to that point where the bows start pushing side ways and the rudders start cavitating.
The fastest I've sailed was on a H16 solo, broad reaching, or maybe a little more down wind than a true broad reach because I was scared I was about to crash. I think the wind was probably hitting 30 at that point. When I came on shore a friend told me that the ranger had come down and warned our fleet to expect 50 MPH a little later. None of this was measured and the only ones to notice were the men collecting the trash a ways up the hill, they commented that they hadn't seen a boat sail faster. As the rest of the fleet decided to go sailing they went three and four aboard their h16s and h18s.
I hope you brake the sound barrier.
Will