Time is more precious to me than the fuel savings. I always have a trailer & I drive 70 mph +/-
Life is more precious to me than time, so my usual interstate speed is 60 mph. If I notice traffic is being held up by me, I'll usually take a break but that has only happenedonce. My preferred back road speed is about 50 mph though I don't mind running about 35 either if there isn't much traffic on the road.
I have found I prefer staying a bit closer to home or taking more time to get there.
And yes, I still work full time with limited travel days.