Here’s an interesting video where they used a high-speed camera to slow down shots fired from 3 guns, similar in every way but their chambering: 9mm Parabellum (Luger), .40 S&W, and .45 ACP.
What’s great about the video is almost everything is the same, about as “apples to apples” comparison as you can get. Of course, chamberings are different, and of course ammo but then with ammo he chose “standard” ammunition for the caliber. The only thing I’m unsure about is the human factor: does Andrew have a consistent grip across all 3? And while he probably strove to do so, we’re human and can’t always register differences — too small for us to notice, but big enough to make a difference. Regardless, the video is still useful.
The video points out muzzle rise, but I also think it’s interesting to watch muzzle return. Again, this could be the human factor coming into play, and it’s possible Andrew had no intention of follow-up shots and thus a need to get the gun back on target. But taking the video for what it’s worth, it sure seems that with 9mm you’ll be off target less and back on target faster. Thus, follow-up shots can come quicker (i.e. you become the limiting factor, not your equipment).
So, since all pistol rounds suck about equally, when choosing the caliber for self-defense purposes you have to look at other differentiating factors. This video points out some key factors such as recoil manageability, and how that affects your ability to shoot and handle the gun both in general and in particular situations (e.g. multiple shots). Consider that in a self-defense situation, every tenth of a second matters — do you want things to maximize or hinder your ability to make the most out of every tenth? do you want to ensure every tenth is used to fight and not to wait to fight again?
For the record, I carry a 9.