KE is good, but its not everything. Momentum is much more important with regards to HUNTING. A heavier arrow will always penetrate better. For 3D and target, a lighter arrow with a flat trajectory is preferable, all you need the arrow to do is stick in the target.

For the smallish whitetails in the south, I don't think it matters much. But if you are going after those big northern/midwestern deer or any big game, I would take a heavier arrow in spades. You aren't giving up much by shooting 275 instead of 305. Your bow will be quieter anyway, and I'd rather have stealth than speed.