George, addressing this from your PM also: If you just want one set of good sheets, I like to use New England Flight Line, 5/16". I strip the cover off of the forward sections and taper that back into the spectra core for a very light, very low stretch spi sheets that can handle any wind you choose to sail in but still be light enough for great light air use (tie a bowline, NO snap shackles PLEASE!!!!
), and the 5/16" tails are still easy on the hands. The polypro covers won't last as long as polyester but if performance is what counts I won't use anything on the spi sheets that gets heavy when it touches the water unless it's so windy that it's a moot point.
If I was going with dedicated sheets that would greatly extend the life of the Flight Line, 1/4" would be my choice for light air and Samson Warpspeed in 5'16" would be my choice for the higher stuff. This line is basically bullet proof. Some people are of the mistaken opinion that larger sheets are easier on the hands but there are 4 reasons that I don't agree with that: smaller line ALWAYS goes through the systems easier than larger line which means less effort to trim a given load, gloves, auto ratchets and winches!!! Some might think this to be overkill too as far as stretch goes but I most heartily disagree. If your sheets, halyard, topping lift, foreguy and tweekers/twings are the best stuff that you can afford, the boat WILL get more out of every puff because that's goes directly into pulling the boat instead of stretching the line and THEN pulling the boat. This also means that when you set the pole somewhere it basically stays there until moved. All in all the whole bit adds up to less trimming required over the long haul, BUT, you must remember that the chute is now REALLY the weak link and will take the brunt of sudden collapsing/filling, so the trimmer needs to pay attention!!!
Twice the length of the boat is fairly standard for spi sheets, but someone else may say differently.