IMO, and it just a guess, but heavier seems better.
The line drag is probably a big factor and worse the lighter you go.
Why not add weight to the shaft that you have? First try it at the tip, but if it bend too much and hurts accuracy then add it to the tail where it won't hurt.
You could go under water and fire a shot. See how much line pulls out until it stops.
Change weight and compare again.
Which ever pulls out the most line wins.
Perhaps not a mathematical answer, but it should be conclusive