If you want to make a real holiday of it and add an extra day to your journey. then do go through Foix -- you can spend the night in Andorra. Well worth it for the scenery alone.also..
I tend to drive a lot faster on french autoroutes - far fewer cameras and the further south you go the faster the general traffic gets. you can easily get sucked into 90-100mph without realising it. when you get to the pyrenees, stick to motorway. follow the toulouse to carcassonne route - avoid the mountain road through Foix. looks like a shortcut on the map - it really isn't! the ibz ferry from barcelona is pretty easy - virtually no facilities at the carport though. take your own supplies. it can get very hot there whilst you're waiting.