Living in Colorado, CDOT does a very good job with speed limits.
There are many 2-lane highway signed routes which will give 65 MPH zones as much as possible. But when there may be a steep hill or a stretch of winding road, they will reduce the speed accordingly, but will quickly raise it back up when the lower speed is not needed.
That doesn't mean they are totally smart. There are a few WTF stretches where there is no reason to have the speed so low. Case in point, there is a 50 MPH stretch of CO-82 between Basalt and Aspen with a RIGHT lane HOV lane during AM and PM drive -- just try to stay at or
slightly above 50-55 in the left (Non-HOV) lane during those times without getting honked at, high-beamed or flipped off.