I think Beefy nailed it. Don't worry about the 9mm; it will do the job if you put any decent defensive round in the right place, and placement is easier when you can afford to practice more with less-expensive 9mm ammo. If you're a good shot with the .40/.45, you'll be a GREAT shot with the Nine and some practice. If you're already a great shot with the .40/.45, you'll be a SUPERB shot with the 9mm. There is a reason that many competitions separate the 9mm shooters from the bigger calibers; once you begin to master the fundamentals of handgun shooting, it is simply easier to shoot the 9mm fast and accurately.
Originally Posted by BeefyBeefo
"Placement is power" -- seen in an article by Stephen A. Camp
(RIP, Mr. Camp; you will be remembered, and missed)