45 there and back?
I find around 65 is decent for making steady process and having an ok mpg.
I used to do 90 miles per day, cost me £70+ per week at an average of 55mph/36mpg.
I drove from the nw to the ne at 70-90mph and that cost me £60, the next time I did it I sat at 55-65 and it cost me almost half that