Have me shoot it!
10mm? TOO EXPENSIVE! TOO RECOILLISH!
.40 caliber? TOO EXPENSIVE!! TOO RECOILLISH!!!
I’m actually glad we can argue over the finer points of ammo. It’s better than having to talk amongst ourselves about where to find ANY ammo from a black market dealer. But as I said over at When The Balloon Goes Up, the argument truly is academic.
There are, at my last count, over 32 million factors that go into what makes a particular shooting effective, 7 or 8 of which you actually have any control over. All firearms are a compromise. Handguns are small for portability and thus lose the ability to get the bullet travelling fast (velocity is king). So we increase the mass of the projectile, lower the weight of the launching system, and are rewarded with shitty accuracy and unpleasant recoil. However, it’s difficult to get a comfortable holster for your 30-06 bambi-zapper.
Add into the equation that an assailant might be wearing a Kevlar cardigan or a particularly thick leather jacket, is pumped up on illicit Flintstone vitamins, the rotation of the earth, a rib, the fact that while you are shooting you’re also tripping over your own feet, the assailant is offering your a free Columbian necktie, Mars’ alignment with Venus, and any number of other factors, and all of a sudden the 9mm vs. .40 vs. 45 debate just seems a bit silly.
Carry as much gun as you can reliably handle, that you can afford to practice with, and that you are comfortable with relying on to save your life.