I'm not sure about who all has been timed the fastest since the advent of electronic timing, but I did see that Jose Altuve and Billy Hamilton were timed on a bunt, from the right handed side, in 3.3 seconds a couple years ago. As for Deion, I remember he used to steal bases standing up with no slide quite often. Bo Jackson was also super fast on the bases.
Mickey, in today's modern game, with all the year-round training, nutrition experts, physical therapy, etc....would be unbelievable to watch play. If you think about it, with the way he abused his body with all the drinking, drugs, carousing, etc....and so on, there's no way he could get away with that today with a tightly monitored as the players are now. Plus, with his injuries, he missed a lot of games per year, over 20 games per year on average. Today, I doubt he would miss as much if he took better care of himself and had access to all the advantages that athletes have now.
He would put records so far out of reach that nobody could catch him. Oh, and with today's ball parks with smaller dimensions, his home runs would be off the charts. I also think that he would still be the fastest man if he played today.
And was Mick timed batting left or right. Left, he would have been quicker, since he would have been 1-2 steps closer to first.
It's fun to imagine what he would be like.