It will depend on how good your endurance is. If it is good 0.8 and Ok 0.75.
The most important thing for me would not be to go too far over 0.8 IF early on.
I have gone 0.82 for 7 hours no stops 0.83 with stops.
I have gone 0.84 for 5 hours no stops.
I have gone 0.91 for 3 hours no stops.