Thanks for the responses guys, much appreciated...............

I`ve done big miles before x2 500 mile days and x1 730 mile day, albeit a few years ago.
Its just that I`ve never done that sort of mileage on foreign soil on strange roads.
Wherein lies your problem, perhaps.
If you come off the motorways, your average speed will drop dramatically. If you then come off the N (National roads) onto D (Departmental roads) it will drop again.
We did Calais to Algeciras and back (twice) on the Moroccan Dashes, in two days, via motorways all the way. We also did Budapest to London in one day, again on motorways. On lesser roads we would have struggled to do it in the time.
I have done Calais to southern Spain in three days on lesser roads (on a Blackbird) but I lobbed in chunks of motorway to avoid what were simply straight National roads (often running parallel to a motorway, so no more exciting) and to cut out major cities. I broke it up into three, nearly equal, thirds:
Calais to beyond half way down France, on day one.
Half way down France to beyond the top thirdish of Spain, if you see what I mean. Day two.
Just under 2/3 of Spain on day three.
It wasn't too bad but I didn't stop for pictures and took coffee / lunch stops on the hoof. Did not camp but stayed in small private hotels, booked in advance so:
(a) I had good daily targets to aim for.
(b) I didn't have to ponce about looking for a bed, wasting time.
Have fun.