I've only chronoed up to 14 GPP but at least up to that point,momentum was going up.
Here are some figures for a 51# Bear TD with Rose Oak limbs.
1.714 gr arrow,155 fps,14 GPP,momentum .49
2.619 gr arrow,165 fps,12 GPP,momentum .45
3.530 gr arrow,175 fps,10.39 GPP,momentum .41
Going from lightest to heaviest that's a 12.9% loss of speed and a momentum increase of 19.5%
Fred Bear did impact testing up to a ridiculous 18 GPP and found impact increase all the way up to there.But,he liked 9-10 GPP,because of the balance that we are talking about between trajectory and penetration.He also took very long shots at game,at times.
I think you just have to decide where your personal balance point is and what kind of trajectory you need or like.