Do you have a repository of write ups of self defense uses by concealed carry people? I sometimes see a writeup of where ccw'ers have used their guns but I seldom see any reports on the number of rounds fired. The ones that were killed because they ran out aren't very vocal either.
Seriously though I've never seen a good compilation on the data of concealed carry weapons use, I'd love to see it if you know where to find it.
That said to answer your first question a 1994 robbery of beverly hills jewelers in richmond virginia where the owners had 11 snubs, 1 .44mag, and a 12ga. I believe the owners fired something like 30-40 rounds during the robbery defending themselves against 2 attackers. Thats certainly the extreme scenario, but I'd personally like to see numbers. What percent would we be comfortable with? 85% don't require more than 9 shots? 90%? 95%? We're already preparing a very unlikely event.
For normal defense cituations it is more than enough. But if your in a full blown shootout I would perfer something else. Glock 34 anyone?
I have a friend that is an engineer, the mechanical and structural kind, not the train kind, and this is what he told me. A spring held at maximum compression will relax more over time than a spring that is cycled between high stress and low stress. The reason being that the spring spends more time at the higher stress level. Also humidity and temperature factor into spring relaxation. He also said that a springs failure rate is directly related to the tempering process when the spring is manufactured. My experience is that I have had several magazines that have been loaded for extended periods of time and the springs have weakened significantly, not to the point of malfunction but enough that I would not risk my life with them. Your experiences with magazines may differ from mine as may your opinions.