I've done some research into this many years ago and from what I recall, they were virtually identical in chemistry and manufacture, except that dyneema had one more process that made it less brittle. I've heard many people claim that spectra has snapped on them when the load "bounces".
I'd almost consider using Vectran for all fixed rope systems; no creep, good toughness, abrasion resistance and UV resistance plus I think it actually gets stronger when knotted!...Will have to look for a price next time I head to the chandlery. Vectran
