This isn't being said for Chris, but moreso RB's in general ...
Speed is great for hitting home runs, but a RB needs vision and good feet before speed.
RB's generally aren't running full speed until they get into the open field. In order to get into the open field you need vision and the ability to navigate through traffic in the tackle box. (which is where feet and wiggle come into play)
The hardest RB's to defend are the ones who can make you miss in a phone booth. Gore had a ton of long runs in his career and he was never a speedster. Duke was the same way.
A RB doesn't need 4.3-4.4 speed to hit home runs. I would bet that the majority of elite RB's we've seen over the years are somewhere within the 4.5 range.
Most running plays take place within the tackle box. Close quarters. Things happen very fast. If you can't make people miss in tight spaces, you're not gonna be very successful IMO.
This is what made Hankerson at STA so tough to defend. You could have every gap covered, have him bottled up, and he would make your LB whiff at the LOS and get positive yards.