There are still lots of places where the interstate speed limit is 65. If so, then 60 is ok.
But for lots of open road travel, its true that one will often be on roads with 70mph or higher. In that case, it is true that one becomes a traffic hazard. If I don’t want to go past about 60 for any reason I just don’t take an interstate. Most of them are built right next to alternate routes. Of course, we don’t know if the OP is on interstates or not.
As for the MPG, just try to always drive it downhill.