That is surprising Wayne. "Everybody" I have been in touch with so far has advised against synthetic shrouds and forestays.
How do you adjust the stays, and tension the rig? Have you bought some of Precourts fittings, or do you have your own solution?

BTW: We have used spectra lines as trapeze lines for.. it must be 4 years now. Even with 110kg's on the trapeze and jumping from wave to wave they have been solid.