I had a pair of Sullivan Kevlar ( aaramid ) lines 10-12 years ago. Tried them on a profile trainer ( Streak trainer maybe - solid balsa airfoiled wing about 32" span) with a pretty good Fox .19 on it. The lines had so much drag ( wind resistance due to large diameter/ flatish cross section) that they had a 6-8 foot bow between me and the wing tip. Very mushy response and plane was slowed down a bunch. Switched back to regular .018 stranded and it was like a new plane.

I agree that you should probably use them for reinforcement. Might make a good spar cap stiffener or sandwich between top and bottom trailing edge sheeting to stiffen that up.