[Christ]

It took him about a month or two worth of fuel (2-3 tanks a week) of "testing" all highway driving at different cruise speeds. His was an automatic, so no real gear selection issues or anything there, he just found out that at ~62 (indicated), he got the best fuel economy, with a notable drop (~1mpg average) between ~62 and ~55, as well as between ~62 and ~65-67.

He did note, though, that if he were ever in a hurry to get to work, that ~73-75 was a "good compromise" between speed and efficiency... I can only assume that meant the fuel economy wasn't that much lower (2-3MPG, ~10%), and that the speed was high enough to make enough time to "forget" about the MPG loss.

Lest we forget, for some people, slowing down to get better MPG actually costs them more in the long run... If you make $30 an hour, and you're taking an extra half hour to get somewhere because you're going 5 MPH slower, you're losing $15 in wages... and gaining a few dollars in fuel (if that). In fiscal terms, the best fuel economy isn't always the best policy.