How are you getting a length of 140'-150' for your halyards? As even with a tall rig, your hoist is 47'. So 50' x2, plus 15' from the spar base to the winches, & 5' for the splice = 120' per halyard. Non? Which actually gives you some extra.
And when I looked up line prices at Defender, the MLX equilavent as per recommended by Samson Rope
is 11mm (7/16"). Which is the same price
as 3/8" Warpspeed, at $2.29/ft
So the math fully makes sense. I wasn't aware of the large price
differences for your locale however.
Since you're more desirous of good shape in the new jib
, then just do that halyard now. And leave the main halyard alone until next season... after things have thawed out.