MMM 21 feet ..thats 7 yards....thats 7 steps= about 2.1 seconds = the average draw
a 4.4-40 is really fast....; )
Glad your Ok
On this note, some defensive training would help too.
Take some basic Tae Kwon Do. It teaches you a core set of defense techniques which would play into this area. A great technique for this would be to use the persons energy against them. As they charge you, you center your mass and when they are one step away, in a fluid motion step to the outside, grab the wrist and rotate your body insuch a manner as you force their arm to rotate with the palm facing up. This naturally causes the hand to open and to immobilize their hand and arm. They will drop the knife and you have full control. You can continue to roll the arm in the "police method" to lock it behind their back and then perform a take down.