For a jib
halyard on a roller furling
foil, stretch really isn't an issue. You will have little problem maintaining enough tension on the luff for proper sail shape. 7/16" StaSet X would be more than strong enough and easy on the hands for manually hauling up the sail. If you want to spend a bit more, New England
ropes VPC gives the low stretch of a bit of Vectran but less costly than the all Vectran cored line. It also isn't as stiff as StaSet X so easier to handle.
If you are one of those anal racer
types willing to spend big bucks to get lowest stretch, lightest weight halyard and have a wheelbarrow full of money, go with Samson
Warpspeed or NE V100 in 3/8". Of course, if you are really anal, do what Stumble says. The lightest set up but a real finger eater for manual hauling.
Keep an eye on Ebay, rope clutches
turn up all the time for $50, plus or minus. If the winch is also going to be used for other halyards, that would be my first acquisition.