10point; It's not that simple. As chopinbloc pointed out, a hit in the leg
may kill someone, if it severs the femoral artery. But it takes @ 30 seconds to bleed out to incapacitation (shock anaphylaxis), and in that time, it is possible they may continue their attack. A hit in the
vitals (as you quaintly put it)
may, again, kill someone, but again, it is rarely instantaneous, and not 100% sure.
From your username, I assume you are a deer hunter; I am too. Let's examine why we aim where we do at deer, and the circumstances in which we shoot, and see how they relate to human incapacitation. I aim at the top of the aorta. The reason I do so despite CNS shots having the highest percentage of fast stops is that the CNS is a small target on a deer, well protected (the head) from most angles, we generally aren't shooting them at less than ten yards, and the top of the aorta hit causes bleedout to incapacitation very quickly. (But again, up to 30 seconds. In that thirty seconds, I had one buck run 75 yards and hide under a log. We'll revisit the reason why in a minute.) If i am a little bit off, I hit lung for about 3" any direction I am off. Again, the deer might run, but I'll be eating venision. This is the most ethical shot for deer, the aorta, IMHO.
People are not deer; Deer haven't been told by TV and movies to die when shot, like humans, nor do the ingest chemicals that reduce pain response to keep 'fighting throught it'. (I'll get to adrenaline in a second.) Many deer just drop from a well-placed shot, but not because Hollywood taught them to. (Despite Bambi's mom..) It's because they are not under the effects of adrenaline. Some deer are under the effects of adrenaline when shot; their usual response is to run fast, tail down. (Not bound, tail up, as when alerted.)
As with deer there are many variables to incapacitation of humans. One added that deer don't (generally, though there are exceptions) have is attack intent; A human with a 'mission' to attack you and adrenaline coursing through them is a formidible adversary. (Think 'Berserker rage'.) They will take hits and keep on coming, hits that would drop someone who is just sitting there, drop them like a sack of potatoes. A femoral artery hit on such
will kill them, but it may be a Pyrric victory, as they might well have killed you in the time it takes for them to be incapacitated. A "vital" hit
will most likely kill them, but again, not quick enough to help you. A CNS hit has the highest probability of the quickest incapacitation. The more penetration in that hit will increase that probability. Bird shot to the skull is not reliable enough, I have seen the results. A guy I grew up with shot himself under the chin with a AA Trap load attempting to kill himself. He succeeded, but it took two weeks for him to die. The results were not pretty.
Chopinbloc, I agree with you, but I do have to point out; If the FBI is the authority on penetration, how come they keep switching rounds?