I can't remember who wrote the spreadsheet, but if you read this - remind me that I owe you a very large beer.
Spreadsheet said I'd do 76:03 and I did 76:44, so that was pretty close.
If it was mine.... it didn't work for me!
I overestimated the much-talked about effect of the 'fast start', underestimated the time needed to get through busy controls, didnt allow time for roadside stops, didnt account for the p.m. start (of which had no experience anyway) and the resulting sleep deprivation almost from the off, but fortunately my moving speed dropped off much less over the days than predicted.
The big lesson learned - sleep deprivation kills speed like nothing else, short cat-naps are fine for dealing with the dozies but don't help with the speed, better to get a longer sleep sooner, leave a control out-of-time (even by a significant margin) if necessary, and make up the time on the road.
I'm on film as saying I'll not do it again, but if I did I think a sleep at Villaines on the way out might be effective from pov of reducing sleep deprivation and hitting subsequent controls at quiet periods.