I was at the dog park the other day, giving some R&R to the Catican Guards, and was noodling around on my Droid2. I decided to look up the most efficient speed for the FredMobile (a Nissan Altima) and came across this link and this chart.
It turns out that at lower speeds, fuel economy is dominated by your RPM and gear ratio. At higher speeds, wind resistance is king. Recently, I've tried setting my cruise control at 65 MPH on longer freeway trips* and I've discovered that the car seems to feel better at that speed than it does at 70+. At the higher speeds, it feels like its straining.
* - and also when I want to have fun just tooling around the neighborhood. Man, that Wilson kid can run!