Max theoretical is actually 81. Helf can get 1 more int than drow through action surge. Max int with drow is 85, with helf action surge it's 86. You'd have to spend 15 points in helf tree, 22 in mechanic, and 41 in assassin. So it would eat up most of your points, but it's possible. So as far as I can tell, this would be max:
10 base
20 rogue levels
6 stealthy (shadowdancer tier 1)
2 EMG
5 measure the foe
38 int86 (18 base, 5 tome, 7 levels, 1 human adaptability, 1 arti dil, 3 action surge, 2 capstone, 2 assassin, 2 mechanic, 11 gloves of the master illusionist, 3 insight, 1 exc, 2 yugo, 2 ship, 6 epic destiny, 3 twisted, 3 great int, 2 completionist, 1 litany, 2 store pot, 3 house D pot, 4 abashai cookies, 2 bard song)
81 Theoretical Max Assassinate DC
Also, if anyone is looking for gear suggestions, I list mine
here. There is a lot to fit in. All I'm missing (some of which isn't completely necessary) is seeker, threat reduction, heal amp, doublestrike, and open lock. I'm open to feedback and I'd like to hear what others are planning for gear.