Saturday and sunday drivers tend to be a bit slower, most of the time because they've had a drink the night before from what I see when I drive on the roads.
They may or may not still be over the limit but go slow in case, or perhaps because of a headache from it.
People who stick at one speed usually are bad drivers or over the limit, unless that speed is the speed limit.
I was behind one once which did 45 on every road, including 20 and 30, no speed deviation.
They had no observation or clue which made then very dangerous.
Some NSL roads should not be NSL though, I will go slow on some country one near here due to cars parking on, horse riders, cyclists and pedestrians.
Plus there are blind bends.
The numpties are the ones trying to hit 60mph and then almost causing accidents there.