If you do decide to drive in August...
I have found driving long distances (7 hour drive) in France on a weekend in August have become better since I learned to happily use a squatter toilet at the small service areas with just toilets and parking, instead of relying on those at the large service areas with food and petrol. Plus, I also take all the food and drink we need in a cool box.
This means we can avoid the battle to find a parking space, toilet queues and food queues, and have a more relaxed break at the small service areas (these are still very busy on August weekends). If you are driving over two days I admit you might find it a challenge to keep food cool enough for day two...
Don't stop on the motorway to fill up with fuel if possible - I learned that lesson the hard way after sitting in a hideous queue on a Sunday in August. Instead top up when you stop overnight.
I have the badge to pay for the tolls automatically, so the queues are much shorter. If you don't have the badge, I have noticed that the queues are significantly shorter for the pay booths on the left that are not manned and have a height restriction, compared to the manned ones on the right that all the caravans and campervans have to go through.
Pre-book your en-route accommodation. We always stay in an Ibis just off the motorway on the first Friday night in August. I am always amazed at the number of people I see when checking in who haven't reserved anywhere and ask if there are any rooms available and are surprised at the negative response.
And finally, don't forget to take some tissues and wet wipes with you when you use the motorway toilets.... 