I pick 85 because I feel by that point any viable solo hell build should have been able to kill Baal. I did complete the game legit (every quest, no rush) with some build under 80 but I taught 85 was a safe number.
Only my Mf build and my Smiter are higher than 85, all the other one are below 85. I did the walkthrough with them for fun and went back to my main character after.