We sort of went over the same topic in the Revolvers section just recently--mainly how much capacity is needed for defensive purposes. My answer is still the same: I'd rather have more rounds than I would need than less. There are other factors to consider as individuals, to be sure, but that about covers capacity for me. Even if I can make each shot count, as I intend to, multiple shots on target is better than fewer if all I have is a handgun as opposed to a shotgun. If there is only one target, then I won't need many rounds, but if there are multiple targets, then I'd want to have a bunch on hand--within reason, although 7 per magazine is kind of on the low side, especially since I'd prefer to avoid reloading if possible.
Am I the only one who thinks caliber doesn't matter?
It doesn't matter much in the grand scheme of things, but it may make a difference in some cases. A good rule of thumb is to shoot the biggest caliber that you're comfortable, accurate, and fast with, and then bump it down if capacity is an issue for you.
Obviously I am not going to war with a .22
Well, I guess caliber does matter, then.
but any decent shooter should be able to put someone down with anything
That's right, even with a .22, although they won't have as good a chance against bones that may get in the way, for example, and will have a somewhat reduced chance of hitting something vital. Then again, if such a light caliber makes some folks better shooters, then it may well be worth the trade-offs.
The general question here is whether a larger caliber is worth the trade-off of a smaller capacity, and it's a difficult one to answer because the former only helps a little while the latter is rarely an issue for civilians. Maybe that's one reason .40 S&W has become fairly popular even outside of law enforcement--those who can't decide might as well split the difference and be done with it.