If you are using the autoroutes to cut across the top and then down via Bordeaux, you are missing out, unless you want to get to Spain quickly, and it depends on what interests you. The St Nazaire to Gijon ferry is currently nearly fully booked for the next three weeks ( unless you want a 4 berth cabin), I 've looked today because I'm planning a trip to the Asturias for the end of Sept. Cutting down via Chartres from Calais(to the north west of Paris) can lead you into the Loire Valley and Chateaux country, and then further south into the Vienne ,Haute Vienne and the Poitou Charentes the roads are traffic free and really good to ride, beats the hell out of the expensive Autoroutes.
I live to the south west of Limoges, and from here down through the Dordogne and the Gironde are good roads but not much to look at except the vineyards. South of Bordeaux the 'Landes' department is flat and pine forest and then you are into the foothills of the Pyrenees pretty quickly and the Spanish border.
The west coast route down via Nantes , la Rochelle, Royan to Bordeaux is actually IMHO pretty boring and not the best part of France, although the Ile de Re and La Rochelle are worth a visit.
Have a good time!
