"Get someone to charge you from 7 yards (21 feet) or less intending to kill you with a large knife or a baseball bat. It'll take them less than 1.5 seconds to cover the distance (see Tueller drill). How many times would you propose to shoot at them in the hope that they will stop?"
I propose that the solution to such a problem is not simply drawing/shooting fast. That's one point of the Tueller drill which is often overlooked. (I've discussed this with Dennis personally, BTW)
The goal isn't to "win", by shooting him X
number of times before he reaches you with the knife. Aside from the extreme unlikelihood that one would be able to draw and shoot quickly enough, that simply means that you get off a couple of good shots before he starts slashing/stabbing away at you in what might be his last minute or so of life.
If someone is running at me with a knife, I'll be running the opposite direction while drawing and shooting. This solves the (more important) problem of not getting
hurt, while putting out a lot of hurt in return.