It seems my engine loves the 57-59 range. No hard data, just experiencing it. I could be wrong.
Your engine will have a sweet spot, too. Often people think it is 65+, and I don't know why. I am sure I am more efficient at a much lower speed, but 1400 RPM in 6th runs pretty smooth for me. I use cruise, but do so carefully. I will cut it for down hills, or when I want to accelerate for a nice coast, or ease off the throttle up a hill when I will be gaining it back for free on the other side. But for general flat/no intervention needed driving, cruise will use as little fuel as possible- good with me
