This has been around a while, but there's some good information on how your common pistol cartridges stop someone here.
Basically, they don't.
Ok, so what would give me that edge?
There are some cons to go along with a bigger caliber, so that needs to be considered too. (Cost, size of the gun that shoots them, fewer rounds, etc.)
Basically, they don't.
Physiologically, no caliber or bullet is certain to incapacitate any individual unless the brain is hit.Having said that, it's not true that some cartridges aren't better than others.
The much discussed "shock" of bullet impact is a fable and "knock down" power is a myth.
Although no cartridge is certain to work all the time, surely some will work more often than others, and any edge is desirable in one's self defense. This is simple logic.
Ok, so what would give me that edge?
The critical element is penetration. The bullet must pass through the large, blood bearing organs and be of sufficient diameter to promote rapid bleeding.I'm not going to say you should always use this particular caliber or that caliber sucks, because for the most part there are only 3 pistol calibers to choose from and they all work about the same (not very well), but there may be some benefit to choosing the bigger caliber.
Given desirable and reliable penetration, the only way to increase bullet effectiveness is to increase the severity of the wound by increasing the size of hole made by the bullet.
There are some cons to go along with a bigger caliber, so that needs to be considered too. (Cost, size of the gun that shoots them, fewer rounds, etc.)

