In my experience this results in more people trying to pass because they don't have too much extra time to go below the limit. More passing equals more potentially dangerous situation, at least if there are no extra lane and passing is on the oncoming traffic lane. So there's at least one downside imho.
I'm with you minus the driving below the speed limit thing.
Why would you do that?
Literally zero down side and it's safer.
In my experience this results in more people trying to pass because they don't have too much extra time to go below the limit. More passing equals more potentially dangerous situation, at least if there are no extra lane and passing is on the oncoming traffic lane. So there's at least one downside imho.