From the small dodgy data I’ve observed, the exp required to advance each level varies with the square of your level. (mainly at level 59, it took about 160k, at level 30 it took around 40k).
If that’s true, you get roughly half of your XP at level 80, about 2/3 in.
But take into account that you would want to be reborn at level 60, which would be at rebirthed level 72, about 90% in.