No, the "speeding" part is from my own experience. The speed limit here in Wisconsin is 70MPH, but hardly anybody follows it. In any case, a driver who cannot handle a 20-25MPH speed differential should not be on the road, period. Most people can't even handle going that speed on residential streets, it's that slow. I propose the following thought experiment to make it obvious:

Two identical highways, both empty. On one, the U-Haul driver following the company's 55MPH speed limit. (Minimum speed on 70MPH highways is often 45MPH, by the way.) On the other highway, a driver following the speed limit at 70MPH, but is who cannot handle closing in on things at 15MPH. Distraction, eyesight problems, who knows? The slow, 55MPH driver will have no problems. The faster driver has a high likelihood of crashing into things, even without slow drivers in the way.

If speed differentials are that much of a problem, then it's the faster drivers that are the source of it, and the speed limit is too high.