having a knife or not it is all still very relevant.
'scene from police survival shooting'
in 21 feet or less there is barley or not enough time to defend yourself with a gun.
somewhere around 10 ft don't even try to draw until you can gain some distance. it is interesting to see that you have 1.5 sec or less to decide. providing the person is not hopped up on drugs which will rude that time.
if your impatient see time 8:00