I dont know how up to date you are on French speed limits and enforcement so please excuse me if I am "teaching granny to suck eggs"
In summer, and I dont know when it ends, the posted 90 limits stay posted but are reduced to 80. The old rule was that speed limits reduced automatically to 50 at the sign for the town and went back up at the sign for leaving. In many cases now there is a speed limit sign as well and that might make you think that the old rule no longer applies. It still does. There are tales of confiscation of licences and even of cars if you really give it some but even visiting le Mans when you would expect les flics to focus on the boy racers, we didnt see that many police patrols - bit like the UK. So the tales are true but the risk is not great IMO.
Sadly the roads that once were empty are now crowded. Not as bad as the UK but enough to irritate.
