the myth when he was in school was that he had sub-4.3 speed. Which wasn't close to true. There are guys in the NFL who are that fast, of course, but Ronnie wasn't one of them.
Like a lot of special "speed" guys, Ronnie's finesse set him apart probably more than his speed (which was very good — sub 4.5 speed is of course very good speed). His ability to turn it off & on & to take hard angles without breaking his gait or running form seemingly at all — it caused a lot of defenders just as fast as him — to get stuck in the mud & blown by.
But of course you already know that. You remember full well how he made it look easy in the open field. As if he were only going half-speed (which was really more illusion than reality). His long strides were pretty unusual for the type of runner he was.