I need to make an estimate of where this ride sits between
very very tough, and
totally impossible in 75 hours.
A big factor will be the facilities en-route. I had a little experience of audax in remote areas on the 2014 Scottish 1300; this will be much harder terrain, leaving much less time margin for all the non-riding aspects. Worse, I have very limited "feel" for the region; Scotland I knew a bit about, and could research quite effectively.
Are there any discussions of the route en francais? Or other information sources?
( Previous ride reports mention the secret controls being great food/water depots. I'm thinking this is almost useless info in terms of planning! )
Nowhere near totally impossible in 75 hours.
I did it in 2012 in 74.5 with half an hour to spare but I "lost" at least 7 hours (and spent at least 8 in a hotel but that was intentional).
Would have been sub 70 easily if I'd not lost time in the last night.
You were similar paced to me to durness, I was probably slower then than in 2012 but not massively so.
The main precaution you need to take with the remoteness is stock up on food for the night in afternoon/evening, best do it sooner rather than later. There is nothing open at night, can be pizza places open in the evening but once you've got rations to keep you going all night you can then stop worrying about it.
The ideal hotel point would have been about 650km in 2012 (I stopped at about 600km on the dot and got there about half 8pm IIRC) so if was booking might go for a bit less than 600km what with the galibier...
The picture of the galibier looks terrifying. Hopefully the bit with the sheer drop on the right is wider than it looks!? Never used to like sections like that when I used to do MTBing.
Not decided yet if i'm going to do it again but (and personal preference obviously, but ) I wouldn't dream of driving all the way there...I once drove to provence and even with sharing it with 2 others doing 3 hour "shifts" behind the wheel it was bloody tiring.