Strangely enough, I’m doing exactly that in September – a week with Doug on the Basque coast, then a few of us are planning on spending some time in Ainsa. Maybe also a little riding on the French side as well.
We drive Calais to Irun every year. Unlike in the UK, if you’re on the toll roads, on Cruise control at the legal limit, you nearly always make or beat google’s estimates. The only time you lose a bit is if you hit a big town at rush hour (the toll roads don’t by-pass everywhere – Paris and Toulouse being the most problematic).
Our regular routine is to take a 10/11am Eurotunnel, then spend about 8 hours on the road on the french side, overnight at a cheap Formula1 hotel or similar, then a relaxed 3 or 4 hours the next day to get to Irun for lunch. We pull off the toll roads and find a supermarket to fill up with fuel and buy a picnic (easy with a Satnav to find one that’s not far out of your way), then stop and eat at the road side rest stops. (takes a bit more time but, like the UK, you pay a big premium for fuel on the autoroutes).