We did the Calais - Tours route last year. I checked the Route and went via Paris - driving was fine though very boring roads. On our return we hit Paris late afternoon on a Friday and got stuck in traffic for about 2 hours.
If you are travelling around rush hour time I would say avoid Paris, and if you want some scenery whilst you drive maybe it is better to go a different route, take a little longer and have a more enjoyable drive. Thats what we would do next time!
http://www.viamichelin.com as the other poster said is the best route finder fro France that I have seen.[/url]