Hi Phil,
I currently have an 8mm tapered sheet for my main and jib. I have got a lot of the new Marlow Excel Fusion on my Kestrel which is the funky looking stuff. It seems really good stuff as it doesn't twist or absorb water, and the outer and inner are both dyneema so you don't get any real creap.
I can make you one up if you like, I'll charge you for the rope but you can pay me for the splicing in a beer at the next event if you want. Just let me know how long you want it. As an idea of length, my taper sits at about the mast when the jib is in hard, and the cleat is just behind the daggerboard case. Depends how the rest of the bridle etc is rigged how you have the rest of it.
If I re-rig mine I will go for a cheeky 2:1 inside the boom and then lead it out to a split tail bridle at the transom!