An example of knock down power being irrelevant that I can think of is a good friend of mine who was a 19D/Cav Scout during the Invasion of Iraq in '03 and deployed again later in '05. Many of those guys had 1911's of some form that they picked up over there, and had magazines shipped to them whether we choose to believe it or not it happened. I've heard of incidents where these guys emptied all 7 rounds into insurgents at less than 5 meters to contact and them still not going down, yet one bullet to the central nervous system using an M9 is sufficient to drop them in their tracks everytime. Shot placement is always one of the most important things in combat.
Any idea why those soldiers were engaging insurgents at conversational distance with a 1911 and not their M4?