N230, I think.  We've done it a couple of times now, there and back, and stayed overnight in Perigueux (having arrived in Calais at 9am ish) we've usually arrived in Tortosa at about 6 or 7 the following evening I think.  It's a lot less miles/km than going via Perpignan, Barcelona etc but probably best if you have a GPS or a reliable co-pilot  :)