The comments "relaxok" made amuse me a bit after I drove home from Jacksonville to the DC area yesterday via I-95 (and Virginia's I-295). Back when those roads were posted at 65 mph I generally set the cruise control at 75 mph unless there was enough traffic going faster to mean that I wouldn't stand out going faster. Now the majority of the route is posted at 70 mph, but I still had the cruise control set at 75 mph for most of the trip (again, some portions at higher speeds when there was more traffic). I commented to my wife that the advantage of the higher speed limit is that I didn't give a damn whether I saw a cop (except in Ridgeland, South Carolina, where I had it set spot-on 70 mph....sure enough, cop standing on an overpass running radar and using a walkie-talkie to three cop cars further up the road). Unless a cop is a total dick, or you're in a speedtrap town, 75 in a 70 zone isn't likely to get you a ticket. 75 in a 65 may. It was simply far more relaxing not to have to care.
The media want us to believe that everyone automatically goes speed limit plus nine, but I don't necessarily think that's true. I think more people just go what they think is a reasonable speed regardless of the number on the sign. I haven't found that traffic in Virginia is all that much faster since the expanded 70-mph limit took effect last year (indeed late last night on I-95 between I-295 and Fredericksburg I was one of the faster cars on the road, and I had the cruise control set at the speed limit at the time).