I use dynex Dux for the standing riggin on my S 23 and it has 0 creep. I have spliced it many times making rigging for big monos and put it on a test bench to pull out the slack in my splice and can definitively say it has no creep whatsoever. It is heat treated and annealed under load, which makes it really stiff (maybe not the best trait for a leach cord.) It is also expensive. Regular dyneema or Vectran has almost no creep, but Vectran is UV sensitive and should be covered or painted with rope paint. If it is a luff or leach cord it should be fine since it is out of the sun. DUx seems like overkill for this application. I'd go with vectran. Amsteel creeps too much and technora is relatively stretchy (and a pain in the butt to work with)