Hardball, I agree that while COM will certainly be lethal with a decent handgun round, it won't necessarily cause your attacker to halt his attack.
COM hits, even to the heart will only cause massive bleeding and, while fatal, still leaves your attacker with full functions for a short period of time.
The summary of all my mumbo-jumbo is this:
you have to bring enough gun
you have to be accurate
How's that for a blinding flash of the obvious?
My experience has always been that most folks over-complicate caliber selection. Based on all the information I've read, it's actually a pretty simple deal.