I've always been a big supporter of the bigger is better crowd on this until recently. I always carried a .45 ACP, and I always thought smaller rounds weren't effective. My opinions have somewhat changed as of late. Due to an arm injury, I have downsized my everyday carry from a 1911 to a 9mm, and sometimes a .380. Because of this I have been reading up on the real life performance of smaller calibers. Two articles here and here are particularly interesting. In the second article, the author's data implies that there is very little real world differences in the incapacitating effects of handguns all the way down to the .22. If any of you are interested, have a read. I'd be interested in your thoughts.