Old School runs a 155, 140, 95, 90 (or so). I can highly recommend the Ullman 140. It is a rocket between 10 and 18 knots. Chuck knows how to draw a fast sail.
Materials…I went through the whole rigamarole a couple of years ago. Spoke with a dozen sailmakers and two material producers. Came down to this…If you can afford it, go with Flex Kevlar at minimum for the #2 or #3. For the #1, the carbon strings come into their own, albeit at a premium. Pentex apparently has too much give for our ultralights.
For mains, the jury is out on the benefits of carbon or kevlar over racing dacron.