Stop ideas between Sarlat-la-Caneda and Arles

I'm done this drive twice and both times stopped at the canal du midi rest stop. The food is quite good and you can hang out by the canal. The highway is great and the drive was fine both times. I have preferred this route to maximize time in the Dordogne and Provence.

Neither Toulouse nor Carcassonne are good picks for a pit stop. Either might do for an overnight (I'd pick Carcassonne).

Figeac is right on the way. It's pretty nice. My favorite that isn't too far out of your way is Conques. The rest of the way, between there and Montpelier, is ground I haven't covered.

Going down through Toulouse and Carcassonne is further but on A routes so might be marginally faster, not as pretty and charges some tolls.

The route going Via Toulouse and The more rural route via Figeac essentially take the same amount of time. It really all depends on what you want. If you have never seen Carcassonne, I would suggest a stop over to stretch her legs there. You will not find a better preserved fortified medieval town anywhere else in France. It is simply beautiful. You could stroll through the town and have lunch usually in 2 to 3 hours.
Good luck

I spent several nights in Toulouse last summer and really liked it, but for just a brief in-transit stop I'd choose a smaller place.

How about Castelnaudary and one of the restaurants overlooking the grand basin of the canal du midi for lunch and a stroll?

Thanks everyone, these are all great suggestions!