The minor differences in speed that result in major differences in MPG are correct. Another post said this, but I'll put it in colloquial terms; whenever speed doubles, wind resistance quadruples. It's the single biggest factor in fuel efficiency.

On a road trip last week from Texas to Kansas, I drove 460 miles @ 70 miles per hour and got 45 mpg. On the return trip with a nasty headwind, I got 40 mpg. Huge difference.

BTW, speed limits in the rural midwest actually are 70 miles per hour. West Texas even has a stretch of I-20 with an 80 miles per hour limit.

On short trips -- 30-40 miles -- I've found that keeping the cruise control on 65 (vs. 70) yields roughly 1 mpg better economy, with an unnoticeable increase in time-to-destination. That's a good trade.

Also, the lower speed results in lower stress. I'm not on the lookout for cops with radar guns, and I'm not constantly speeding up to pass slower vehicles, since I'm one of them.

Maybe I'm turning into my grandmother, but I sure enjoy driving more, especially because I know that I'm getting to the same destinations I used to visit, but I'm giving OPEC a lot less money to do it.