I think most here would agree "shoot until the threat is stopped" whether that's one or all of the rounds in your piece.
Which would be exactly the correct thing to do.
Here's the point I was trying to make with my earlier post. Booby traps are illegal because they apply deadly force without a human making the decision. The law requires that there be a reasonable human making reasonable decisions operating a deady force tool.
If we program ourselves to always respond exactly the same way to a threat (e.g. draw then fire X shots automatically) then once the engagement begins we become nothing more than a booby trap until our "programmed" shot sequence is over. Certainly we make the decision to draw, but at that point, it's all simply a matter of programming. I don't think that's wise.
Statistics show that over 80% of all self-defense gun uses are successfully resolved by merely showing the gun. What that says to me is if a person programs himself that when he presents his gun he automatically fires, over 80% of the time he will be firing at a person who would have given up without a single shot being fired.
Likewise, another 10% or so of successful self-defense gun uses end after a single shot has been fired whether or not a serious injury has been dealt. If a person automatically fires 2 or 3 shots then clearly at least some of the time they're doing so when they don't need to and therefore shouldn't have.
It's good to practice, it's good to have a plan, but we can't oversimplify to the point that our responses become so automatic that we're not assessing the threat as the situation progresses.
MORE to the point, it's probably not the best idea to publicly announce that if you're forced to use a gun you're automatically going to draw and shoot X shots aimed here and then X shots aimed there, etc. In the unlikely event that you ever do get involved in a deadly force scenario, a statement like that will not back up your assertions that you only used the minimum amount of deadly force required to insure your safety as the law typically requires...