No probs mate
http://goo.gl/maps/i55mm
The idea is to get through France in the one (painful) hit, then alternate between fun days blatting and days where you just need to make progress. I really want to do the Pyrenees AND Barcelona AND the southern tip AND the northern coast, which is why it's so long! It'll be tiring but well worth it I reckon, and the roads I've picked have been 50% what I think looks good and 50% recommended as detours by folks who have been there.
The route abrubtly ends at Bordeux as I'm heading straight back to my house from there, and I decided it was better to leave it off if I'm going to publish it on the interweb.
@Ian: Sorry, I kinda assumed that you'd be doing some blat drives as well and not just point to point (Stelvio excepted). In that case, I reckon you'll be okay on those mpg guesses.
Thanks Dan, if it helps we do Dorking to 50miles south of Bordeaux in 12 hours give or take, early Eurotunnel and 3 or 4 short stops.