I think it's either one of the Sugar Ray's or Roy Jones, and here is my reasoning:

Pernell is obviously out of this because he didn't have much power to begin with, but he was super fast. So, i think the point of this thread is to say, who has THAT kind of speed but also KO power. That speed is highly above average.

Roy jones was SO fast and he was KO'ing guys.. granted he may not have had the BEST opposition early to mid career, but he was still supernatural.

Tyson was huge and very fast for his size, but i don't think it's fair to include a heavyweight in this due to their shear size. so that also disqualifies Ali/shavers..

both of the sugar rays packed a lot of power, but were really known for their speed. thus putting them on the top.