I think with some of these comments we see so often that folks are always preparing for the absolute worst. Fair enough. But let's face it, your chance of getting bushwhacked by a platoon a Marines is pretty darned slim. You know, guys that will just keep coming at you even if you take some of them out.
The overwhelming vast majority of violent attacks that would call for armed self defense are by scumbags going for targets of opportunity. You pull out a gun, any gun, and place a couple of rounds center of mass, center of forehead, or center of gut, your status as a "target of opportunity" drops to near zero and of course if you're doing it right, you're running toward help, calling 911 etc.
I had a police officer, retired, talking to me at the range. He was telling me they are doing studies of shot placement and attack stopping vs lethality. He was telling me that while nobody is advocating it yet, shots low to the gut and or the pelvis are serious fight stoppers more so than torso shots. This of course is the Internet and that, of course, was gun range banter so who knows.
It does however seem to reinforce shot placement over round. If you find yourself if a fight where you need all 15-17 rounds and then to reload, you need to seriously consider just what you are doing wrong (or right if that's your line of work or whatever).