It would seem to me, that regardless of the KE or the momentum, a very important aspect would be an arrow that is flying a straight as possible. Any fish tailing or wobble would result in energy being wasted because of drastically increased friction. Therefore, if someone wants to really maximize their penetration potential, they should tune their bow, so it shoots the arrow as straight as possible.

It occurs to me, that any changes made to FOC, draw weight, arrow weight, etc. would be detrimental unless it results in a more perfect arrow flight. If a person is "shooting darts" with their current set-up, I'd hesistate recommending any change, just to increase KE, momentum or any other physical parameter. If they do decide to increase or decrease arrow weight, or draw weight, then they should be prepared to work at getting that perfect flight again, and it's not always that easy to do.