pretty much any handgun cartridge will take more than one shot to stop a determined attacker unless you have good shot placement.
Basically only two things will cause a stoper to attack.
1) The attacker changes his mind. This can usually be accomplished with most calibers with most attackers. Even a .22 will ruin your weekend. This is the primary way a handgun ends a confrontation.
2) You incapacitate your attacker. Which boils down to killing him, and the method by which you kill him will be some form of shock.
The types of shock are
a) hypovolaemic shock. Basically blood loss due to bleeding resulting in not enough blood to function. There really isn't much difference in the ammount of blood loss between a .40 and a .45 that hit in the exact same location over any short period of time. For the blood loss to be rapid, either round would have to hit something vital (i.e. good shot placement) for the effect to be rapid.
b) cardiogenic shock. This is bsically the same as above, but due to the heart not working. Additionally there is risk of damage to the heart muscles, and thus it being non-recoverable even if proper blood volume and flow are restored through extraordinary means. It's basically meaningless in a gunfight unless someone has a heart attack.
c) obstructive shock. This is basically the same as a), but due to physical obstruction or mechanical impediment to the flow of blood. Might come up ina gunfight, depending on what you shoot, but short of maybe a lung shot causing an embolism, not going to just put someone down real fast.
d) Distributive shock. This is absically the same as a) except it is due to a systemic dilation of blood vessles. It has sub-types of anaphylactic (irrelevant), septic (irrelevant on the time scale of a gunfight), and neurogenic. This last one is relevant, as it is the result of damage to the nervous system causing insufficient blood supply. Once agian, you are talking about good shot placement.
So basically you can shoot someone in a place that will make them bleed out from arterial blood flow, which is going to ammount ot hitting a vital organ or artery, in which case it's the heart pumping doing the real killing work rather than the .05 inches of bullet diameter. Or you can clip the spinal cord, brain stem, or other important bit of nervous system. Which given the squishiness of the human body internally, that .05 isn't making a real difference in what you hit. It's still about shot placement.
About the only other thing that might play a large roll in ending a fight is cripling a n attacker. Which is where you get the school of though of shooting for the pelvic gridle. But to REALLY put them down, you'd likley have to shatter it. Bullets are more likely to create a hole than shatter it.
Even if you do shatter it, if they are armed, you may still be at risk.
The current thinking on defnsive rounds is that you need sufficient penetration to reach a vital organ to have a chance. The current rule is 12" of penetration. 9mm, 40, 45 all have rounds capable of such. Really high velocity pistol rounds like .454, .44, .357, etc shoudl also be quite capable of this. .380 or 9x18? not so much.
