To my way of thinking momentum is king re: hunting arrow performance. KE is a product of velocity & arrow weight. As arrows get lighter and speed increases, or the other way as arrows get heavier, KE doesn't change much. The problem with light arrows is momentum is much less. Momentum is what gives good penetration. And momentum is a product of arrow weight. Specifically heavier arrows carry more momentum as they aren't slowed down as quickly as lightweight arrows when they meet resistance.