Little experiment with our two cars over this weekend. Pure hwy driving.
2004 Acura TL: cruise control set on 75mph: 29mpg over a relatively flat 30 mile stretch of hwy.
cruise control set on 59mph: 34 mpg, same stretch.
2007 Acura RDX: cruise control set on 75mph: 21 mpg as above
cruise control set on 59mph: 24.5 mpg, same stretch.
Here in NY, @ about 60mph you sit in the right lane and the only vehicles that don't pass you are old pickups driving big horse trailers. But I'm often in no hurry. 34mpg from an Acura TL, a relatively heavy and powerful luxury mid-size car, doesn't suck. Ditto for 24 mpg from a small AWD SUV with a roof bicycle rack like the RDX. Those figures come down quickly once you get off the highway, but a ton of our driving is hwy up here, so we can really skew it upwards by leaving ten mins earlier and driving easy. I've been doing a lot of that. It's rather relaxing. When I'm late I can still hammer down the freeway @ 80-90, but I try to leave myself the time to avoid that.