On Tom Gresham's Guntalk the other day, well I have heard him say this several diff times, that a 45 ACP 40, 10mm, 9mm and 380 all have the same, I'm paraphrasing here, "kill ratio". There is not one that kills any better than the other in a self defense situation. All pistol cartridges are underpowered. I will try to find out where the stats are that he speaks of.
In the gun chambering context he has stated to use what you can control and to get actual training & practice.
Training being an oft recommended subject from him.
Training & practice vs. caliber debate.