75mph seems to be the sweet spot for gearing/engine load to achieve 40-50+mpg hwy!
I've used "Torque" (free android app) to see a numerical instant MPG, including tenths, i.e., 45.1, 45.9 (which I've asked Ford engineers to add/include in next firmware update, they were surprised there was no numerical instant mpg- guess it was an oversight, and other Fords have it? the focus, etc? anyways they tried to find it in the left hand screen...) and thus ascertain the most efficient speed to go up a 5% grade is 73mph=23mpg, and 75mph seems to be the sweet spot (on level ground) for gearing/engine load to achieve 40-50+mpg hwy.
Seems to also be why mpg is higher the faster you go. Within reason. Well, or within air resistance reason. I tested up to 90mph, and wind resistance above 75mph decreases mpg. Unless you were drafting someone else fairly (unsafely) closely (like within 15-20 feet), and that becomes a safety issue and potentially so expensive that a crash would destroy any FE savings.
Granted 75mph is risking your dilithium crystals, (getting a speeding ticket) I prefer to set eco cruise at 65.1mph and let people blow steam out their ears if they get stuck behind me rather than constantly adjusting speed in light L.A. traffic or forego cruise altogether, but given this discovery, I feel more comfortable setting the cruise at 67-68mph or so without fear of ticketing and safe in the knowledge that faster is better/more efficient. Sometimes even 70-75mph if I have a front and back door...