Re: “You are defending yourself from the assailant. It’s best to shoot to kill, as the tale will be decidedly in your favor.” I was told (I believe by a former law enforcement officer) that you don’t shoot to kill, you shoot to STOP.
Example: emptying a .22 pistol into the bad guy is likely to kill him due to massive internal injuries, but it is unlikely to stop him in time to prevent him from killing you. Lots of Moro rebels were killed (eventually) by multiple hits from .38 sidearms, but only after they killed the Army officers in question.
A single hit from a .45 is, on the other hand, likely to stop the bad guy, but it won’t necessarily kill him. I think it was Ayoob who argued quite convincingly that the .45 is more humane because it stops the criminal more quickly, even though it makes a bigger wound than a smaller bullet.
In any event, the objective is to STOP the bad guy from causing you death or serious physical injury, which both the law and common sense entitle you to do.
If you’re firing center-mass or for the head, you’re going to get the kill. The amount of sheer force of a .45 at impact is enough to rupture the aorta or even the heart itself. 9 mm is proven lethal at close range (<5 m) at center mass.
If you go for a gut shot or the legs or groin, you’ll incapacitate, definitely stop, but if proper medical attention is received, they’ll live. I’d rather shoot center mass. That’s my goal when I’m at the range anyway. Largest target area means the highest probability of a stopping or killing blow.