Simon,

I think I read somewhere that spectra is good except where there are tight bends ie. at knots. So it's great in tension but not great in shear.

I suppose you could always set up a double loop at each end so that if it broke at a knot you could have have a safety line to prevent falling off. It might get a bit messy at the harness end.

I think I'll stick with the wire and make sure I always have the ends swaged at the riggers shop.

Regards,

Peter