Andy and Mojo got it. Their answers addressed precisely what I've been pondering. So, if I understand their answers (I think I do, but who knows), I need to continue to practice both at the range and at IDPA to become proficient and comfortable with my EDC so that, if that time ever comes, I will be patient and accurate (but quick). Because I can't know ahead of time what I'll be confronted with, and because what I think is one bad guy could turn into two, or three, or even more, I need to conserve ammo while making every shot count no matter what I perceive the situation to be. And the only way I'm going to get to that point is to practice constantly and consistently so that it becomes second nature to, as MoJo says, "take my time - quickly".
MoJo, your comments made me think of the videos you see of guys in Vietnam shooting from behind a wall. They stick their M-16s over a wall and squeeze off a few rounds without even looking where they're going. Obviously they didn't report to you.
Seabear, your comment about the large cap guys at the steel challenge goes to the heart of my question. Would I be more likely to spray and pray if I thought I had plenty of ammo. Obviously I need to rid myself of that thinking and practice accordingly.
Skiprr, I get your concern, but as I clearly stated at the beginning, this is not about the recent controversy about "large capacity mags". It has to do with training, and thinking and mindset. As Andy points out, well more than 200 rounds may not be enough in the "wrong" situation. (Not that I think we civilians will ever have to experience that.) Since you simply cannot know ahead of time what you will be confronted with, you must always assume you don't have enough ammo (even if you carry 4 30 round mags) and plan your course of action accordingly. Fire as though you are running out of ammo, because you never know when you just might be. There is no worse situation to be in than to get in a firefight and run out of ammo and have a bad guy walk up to you and calmly put one in your brain.