I've been working in Paris for a couple of days....
From Calis to Nice is about 18 hours of riding at a reasonable speed. Dijon is about 6-7 hours riding (not including breaks), less if you hit the motorways. If you opt for the M'way route, your tyres will be shagged by the time you get there (very squared off!!).
We're taking the train this year, motorail down and a 6 day ride back. This may be your best option as you can get there overnight, spend time with the family (riding around the Alps Maritimes - you lucky git
) and then give yoyrself 3 or 4 days to get back via the twisty route... If I were in your shoes that would be my preferred option....
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