For me and the close quarters combat training Uncle Sam gave me, I'd see if the perp fulfilled the deadly force triangle. Which the deadly force triangle consists of; 1.capability, if the perp has a weapon, i.e. gun, he has the capability, 2. intent, does the perp have the intent to use the capability, and finally, 3. opportunity, does the perp have the opportunity to cause destruction or harm to others. If the person fulfills all three of those points to the deadly force triangle, I will use deadly force. As my instructors used to say, Would you rather be judged by twelve or carried by six?