There has been a long and occasionally heated thread -
Driving well under the speed limit: good idea or bad?
This is what I do: stay in the rightmost lane. If someone wants to pass - let them. I occssionaly attempt to anticipate bottlenecks ahead, not only to improve fuel economy, but to allow others to pass me. In the mornings, I leave ahead of the Dallas rush hour.
I drive at about the same speed, but occasionally allow momentum to get me in the low 60s.