Free: Contests & Raffles.
Although I agree the heavier arrow carries more kinetic energy, I do not understand how it could be flatter shooting down range. If that were true, take your set up and shoot an arrow that is 100 grains lighter and see the impact point difference at 50 yards. I would guess the lighter arrow will impact a foot or so higher than the heavier arrow. Find that balance of kinetic energy and flatter shooting.