InSights Training has a surefire post to get the caliber wars running again.
The take away point is this: Round count is largely meaningless as a predictor of cartridge effectiveness without a lot more context. So take what “statistics” you read or hear about regarding self-defense and ammunition with a huge grain of salt!
I can hear the 9mm and .45ACP commandos gearing up now.
The main point to the article is that if you can carry more rounds, you're going to shoot more. The guy with 17 in the mag vs 8 is more than likely going to put a few more BB's in the bad guy. So when you hear about the perp in the ER with 20 9mm bullet holes in him, it doesn't really mean that much. If none of the shots hit vitals, it wouldn't have mattered if those were 20 .45's or 10mm.
The differences in most handgun calibers is academic in nature and just shooting into gelatin doesn't show me squat. If I'm attacked by a bowl of pineapple Jell-O, then that might come in handy. Real situations have clothing, bones, squishy organs, and hollow cavities to mess with the bullet, as well as the fact that you don't necessarily get the time you need to aim properly.
My mantra is carry the most firepower you can effectively handle and do your best for shot placement while avoiding any situation that might require you to use your weapon.