My personal opinion is that it is far more complex than that. For one thing, if an arrows direction changes, even slightly, it's penetration potention is sucked right out of the arrow because of friction on the side of the broadhead, shaft and fletch. This is why it is imperative that an arrow's path remain straight. It obviously won't travel very far if it starts moving sideways, regardless of how high the K.E. is. The loss in penetration when the path is changed, is far more drastic than the reduction in penetration from a bullet going sideways. So, when it hits the animal, the arrow's penetration potential will depend somewhat on it's K.E. but only if it's momemtum is high enough to insure a straight path. When is meets resistance (it always does) it will penetrate best when it's momentum is high enough to keep the path straight. This is why I don't worry at all about K.E. and only a little bit about momentum. Because of how an arrow is designed to work and because of the medium it's hitting (lubricated flesh, with some bone). Blade sharpness is still tops in my opinion when considering factors critical to penetration. I also consider a high F.O.C. somewhat important in overcoming side friction and keeping the path straight.