Based on personal experience (and this is not to imply vast experience or anything
), but you can get a knife and a gun equally fast into action. Yes, you do have to play with the set up and practice it to get it to work right.
Against the "rush", the first priority is not to get the weapon of your choice out, but to respond in such a way to make sure that you don't get killed. THEN, worry about getting your tools out.