Hi Carl,
We recently replaced ours, that had been something a bit stiff and low stretch, like StaysetX. The yard used StaySet 3/8", I think. Seems to work fine and better grip than before. They also replaced outhaul, that was StaySet and soft hand, with the StaySet X. Not as nice to handle. I do not think that the high tech lines are worth it for cruising. On our 380s, and perhaps other IPs, there is a geometry problem that is more important to solve, than being concerned about stretch. Both the outhaul and the furling line change length depending on the position of the boom. The blocks at the base of the mast, should have exit points directly in line with the gooseneck pivot. Right now, the blocks are off center. Someday, I'll fix it. For now, I trim the lines as needed when I change tack.
Fair Winds,
Drew