I though I would share what I have had the opportunity to do recently and to highly recommend it to anyone looking for an adventure with their cars.
There is a route in the French alps called the Route Des Grand Alps. It runs from Lake Geneva, through some of the mountain passes, along some of Frances best scenic and twisty roads and ends up in Menton on the edge of the Mediterranean. A few friends and I did the northern part last year along with a lot of other passes which are not on the official route over four days. This year we did the southern half over five days, again roping in the rest of the passes along the way.
Both trips were 2,000 miles, each of which consist of motorway and A/B roads of 1,500 miles to and from Calaise and hooning around twisty mountain stuff for 500 miles. The other car was a Jag XKR v8 and both cars never missed a beat. The mountain roads host the Tour de France cycling race so the tarmac is like velvet everywhere. We go in the end of September which is out of season so minimal traffic. The last trip gave us most of the mountains to ourselves for hours at a time.
There are loads of filling stations and places to stay at whatever budget you have and we only booked a place to stay around mid day of each day when we knew where we were going to end up.
Highest paved road in France