Actual Maximum Sim Count in a game?

Question 2: I know the game culls townies if you exceed your specified limit (mine's usually 200). It's likely that the same thing happens if you exceed your unofficial limit when you set it to unlimited. 

I can't answer question 1, but it's possible that there isn't one limit that applies to all saves for all players. Other factors affecting the save might cause the unofficial limit to be higher or lower.