My Dyneema jib halyard is not so much about super-high rig tensions, as some sort of consistent tension, without the rig rattling about...
I guess my situation was made worse by the jib halyard, P & S shrouds, and forestay all having cord "make-offs" to tension them; the cord for all this appeared to be still stretching when I got the boat. The shrouds/stay appear to be some sort of Dyneema, so that is perhaps why they settled, but the jib halyard had to go...
I don't use any 2:1 set up, as my BRe has a jib halyard winch (as I think most do?).