I agree with amosgreg, 45# of KE is 45# at 5 yd or 45 yd. I still feel a heavier arrow will penetrate deeper, at the same KE. On deer sized game I don't see the arrow weight being such an issue, as on an elk or grizzly. The deer is much narrower, the elk much thicker across the chest. The elk and grizzly offer much more resistance to the arrow than the deer, slowing the arrow faster. The heavier arrow will resist being slowed better than the lighter one, all else being equal.

Phil.