Power 4.8V servo with 5V?
If you read the data sheet into the first few lines, you'll see it gives 2 sets of specifications. 

Don't be alarmed by the line that says 'ONLY 4.8v' because that applies to the specifications in that column. Those are the figures when supplied with 4.8v.

In the box to the right, it says 'at 6v/reference' where it gives another set of specifications, with higher torques and apparently lower speeds. The word reference suggests that's where it's intended to be used. Why does the speed over 60 degrees collapse from 0.1s to 0.8s at the higher voltage? It probably doesn't, a pound to a penny says it's a misprint for 0.08s.