This was my initial thought. From that era, Willie Wilson, Bo Jackson, Vince Coleman, and Rickie Henderson all come to mind too.
Mind you, pure speed as far as rounding the bases was indeed important - but so was knowing how to cut your path to where you didn't really slow down, plus being able to not stumble a fraction of a second every time you stepped on a base.
I can't remember the exact game, but there was a Cardinals game in the 80's where the bases were loaded with 2 out. I want to say it was Coleman on 3rd, Tommy Herr on 2nd, and McGee on first. Given there were 2 outs, all runners would take off on the ball in play. The batter (can't remember whom) hit a gapper and obviously all runners took off. The defensive relay threw home. Herr slid, thinking the throw was to get him out, only McGee ended up right behind him and scored standing up while having to dodge Herr still on the ground around the plate.
Anyway, they replayed runners on base where you could see McGee gaining on Herr that was hilarious. Herr, while no speed demon, wasn't exactly slow. But when McGee rounded second it was like afterburners kicked in. Herr was running flat out - and McGee still caught him.
McGee was a fascinating player in that you'd watch him walk and it'd look like he was in pain - a very odd looking gait. But when he was running the bases there was no hitch in his giddy'up. Maybe I'm prejudice because I'm a Cardinals fan, but circling the bases he's the fastest I've ever seen.