Be that as it may it was well documented last year and published previously in the Fargo Forum. As you may have noted in the article he was timed, repeatedly and continuously throughout the season, using a GPS monitor device that he was wearing. Other Bison players also wear these devices and they are used for a broader purpose that just recording top speed.
Christian Watson is REALLY FAST---I don't care how he strides---WATCH the games---he comes sprinting from long distances to sprint near ball carrier or block several times on long TD runs! I haven't seen a player CATCH him when he has an angle----watch jet sweeps----and on vertical routes just runs away from opponents.
I'm not going to guess a 40 time but his game speed is off the charts.