I don't know where you keep the tracks, but BG Stats is great for this functionality (and the app syncs automatically with BGG). They have a lot of statistics and charts, based on the players and on the games. You can make some predictions based on the information displayed, although it doesn't show the chances of someone winning.
The official, pre-expansion rule to keep track of 50 points was to lay down the scoring meeple like a farmer.
Start of page 4 of the official rules (pdf):
Note: if your score passes 50 points, lay down your scoring meeple to show your 50+ points
Of course, any way to mark 50+ or 100+ points that your group agrees on and that can be clearly distinguished ...