It is very true that the heavier arrow will most likely get more KE out of the same bow campared to a lighter arrow. But considering that its only gonna get maybe 2 or 3ftlbs at the very most its pretty minimal. And further more consider that there is way more to penetration than having a heavy arrow with 2 foot pounds more KE than a lighter one. You could have a smaller diameter lighter shaft shooting a cut on contact broadhead with a somewhat conservative cutting diameter compared to a lincoln log aluminum weighing 650 grains shooting an expandable broadhead, out of my bow Id put the money on the lighter arrow.