I didn't read all the posts, But like some others said, a heavier arrow retains its velocity better than a lighter one.

If you want to take anything meaningful from KE, figure the KE the arrow has at the range you expect to shoot, for example 25 yds. The lighter arrow will have lost more velocity than the heavier arrow.

I use arrows that are relatively heavy, 29.5" 2315s with 100 gr fixed blade broadheads. They will punch through a deer, even if I happen to hit the shoulder blade.