What WHEELMAN said, I agree with him completely.
I carry a Kahr K40 (.40cal) because it's very reliable and it tucks into my love handles really well. I feel that if I ever have a need to defend myself, seven rounds of .40cal just going in the general direction of the BG should get the job done, hopefully hitting him 2 or 3 times or maybe just scaring him to death. However if the situation ever presents itself (and I doubt it ever will) that I KNOW I'm going to have to defend myself, shot placement becomes much more important to me than concealability so I'd rather have my Glock 19 (9mm) because I shoot it rapid fire much more accurately than the Kahr, better yet I'd rather have the old 12 gauge semi auto.
Face facts, when it comes right down to it, you're going to be scared s--tless, and I really don't think you're going to take the time to worry about sight aquisition. I was taught the 3 to 5 rule. Most gunfights occur within 3 to 5 feet, last 3 to 5 seconds and 3 to 5 rounds are fired. So it's over before you know it and hopefully you will be the one still on your feet. IMHO, in a real gunfight, shot placement becomes a matter of luck rather than a matter skill for the average person.
But on the other side of the coin, if you train, train, train and practice, practice practice, you stand a far better chance of surviving. Ask any Marine or Soldier whose been there, when the SHTF and the bullets start to fly and all your training and practice comes into play, you are scared s--tless but because of your training and practice, your reactions become automatic and hopefully you will survive.