I think your percentages and impression of safety are off. Not sure what part of the country you live in but around here(Boston) going only the speed limit on the highways will get you about run off the road resulting in all sorts of unsafe driving. In other words going the speed limit doesn't make you safe, and going 10mph over the limit doesn't mean you don't care, the safest speed to travel is with the flow of traffic.

Additionally I happily drive well over the speed limit when visiting Maine, 2 lane wide highway, nearly straight, 5 exits in 180 miles and nearly no traffic. A speed limit of 65mph isn't about whats actually safe, its about government bureaucracy (and income from tickets).