Per each player's official NFL Combine stats:
40 yard Dash
Henry 4.54 Dion 4.62
20 yard Dash
Henry 2.67 Dion 2.68
10 yard Dash
Henry 1.60 Dion 1.60
So, in fact, this much larger beast Henry is exactly as fast as Dion at 10 yards, slightly faster at 20 yards, and quite a bit faster at 40 yards. He truly is a freak of nature and it is common to assume he is fast 'for his size' but actually he's fast for any size.
Here's a clip from an NFL.com article listing Henry as one of the Top 8 Most Explosive Players in the 2016 Draft:
Derrick Henry, RB, Alabama
If you're looking at straight-line speed as your only measurement of explosiveness, then Tyler Ervin from San Jose State might be the more appropriate choice among running backs for this list. But consider this -- Henry ran only 13-hundredths of a second slower in his 40-yard dash than Ervin despite outweighing him by 55 pounds. Henry's vertical (37 inches) and broad jump (10-10) were in line with Ervin's (39, 10-10) as well. On the field, Henry's ability to break big runs once in space was a sight to see, as was his ability to go through arm tackles at the line of scrimmage. With the right surrounding cast, Henry's going to be a playmaker.
Derrick Henry = Explosive by any measure