Some time ago I ran a bunch of different weighted "arrows" through a trajectory program I have, from 270 on up to the low 300's, the difference in point of impact is minimal, an inch or so at best. It's one of the ways I'm able to shoot 64#s at 280 without thinking I'm missing the boat
See, this is one of those times when I think I would be better off shooting a 60 lb peak weight bow with a lighter arrow for 3D. Less fatigue, a high speed level and KE/momentum numbers really do not play a part unless you like watching the Mckenzie targets rock back and forth after the shot...
Maybe next year I will invest in a "3D bow" with different specs.