Agree totally about pre-emptive striking being important in situations where violence has become inevitable. However, I would perhaps question whether a powerful fast kick would win a fight instantly in all situations. I believe that the difficulties with employing a kick in such a situation is that if a pre-emptive strike is indeed needed then it is highly likely that the attacker will be very much in our personal space and getting range for a kick may become difficult and require excessive movement to find range. A hand technique would likely be the more achievable option for pre-emptive striking.
Also, going back to my post on high percentage targets for finishing fights (airway, blood supply and conciousness) all of those targets are throat to head height. Throwing a kick with the aim of instantly winning requires kicking at head height. Potentially this may leave the defender vulnerable if this goes wrong.
If we are thinking of throwing a powerful kick to the ribs, stomach, groin or legs then be aware that a very determined attacker pumped up on adrenaline or pain numbing drugs could still fight on through that. I believe that these are all valid targets but should be used with the aim of opening up the more high percentage targets such windpipe, carotid artery, chin, jaw, temples, base of the skull. All more accesable by hand.
Therefore throwing a kick as a pre-emptive strike is all very well but it shouldn't (in my opinion) be thrown as a single strike but should be thrown at low targets as part of a combination to set up the striking of the primary "knockout" targets.
However, like I said in another thread I have met a few martial artists who can throw a kick faster than I can throw a right cross! You might be one of those people thus making my suggestions a little redundant in your case! But I think for the majority using a hand technique rather than a kicking technique is a much more achievable and safer option for pre-emptive striking.
I also suggest that when the decision to strike has been made to blitz the opponent with continous strikes until the threat is neutralised.