Personally I am of the opinion, and through some lecture and training, that the moment someone whom you have identified as a potential threat becomes a genuine threat (ability, jeopardy, and opportunity in the general vernacular) you should not voice any commands at all but rather if you have an opportunity, pull your gun and deliver fire. Shouting commands eats up time, announces your location (unless he is fully aware of this), and can give him reason to believe you are not completely committed to using deadly force against him. I'm not saying there are times when issuing a command is never a good and viable thing to do because there are such times. However, if the threat is, so to speak, in your face like right now, and if you have a chance to get to your firearm, you are better served to use it without reservation and fanfare. Not altogether a simple thing for good folks.