Joe.
We normally ride through France to get somewhere else, this has included Spain, Portugal, Italy, Slovenia, Austria etc.
The D roads are so unpredictable it has been necessary on more than one occasion to abandon them and hit the Autoroutes just to make some progress. I would liken it to some areas of Scotland when it takes an extraordinary amount of time to cover relatively small distances. Although in Scotland there's normally no other choice.
A few years back we decided to take the slow roads enroute to the Dolomites and after a few days around the war graves we headed down to Carcassonne before going over the Petit St.Bernard into Italy. We probably took an enjoyable week to cover the ground and it is so much nicer than Autoroutes. But needs must.
I've got my Crit'Air for this Autumn just because we'll have plenty of time to get to Southern Italy from Luxembourg so may end up in a French restricted area.
Upt.