I had been thinking about this whole "predict my huge histograph score" dilema, and I came up with the following thoughts. I know that SirPleb (I believe) made a predictor tool that works almost perfectly. However, it works only after you reach max territory AND max population.
I think the best way to predict before reaching max population has to do two things:
1. You need to predict the internal score once max population is reached for your map. This can be done using domination limit and information from past games.
2. You need to predict the date at which you will reach max population. This is a little bit harder, but you only have to be close, not exact.
Moonsinger's thread about the map finding gods helped a lot with my ideas. The graphs that she gave were very insightful. The first one showed exactly why SirPleb's calculator works so well. Looking at the following graph (I modified it), there are two stages for "score increase per turn" during the game. During the first stage (A) the change in not very predictable. However, once max population is reached (B), the score increase per turn goes down at a predictable rate. This predictable rate allows for SirPleb's tool to work so well. In Moonsinger's 88k game (yellow) she reached max population around turn 240. In the two 80k games (blue and pink), max population was reached later, around turn 312.
The information that is more important, I think, is internal score. If you plot the internal score for a game, the final game score is the area under the curve divided by the number of turns (540). This area under the curve can be estimated rather easily, by simplifying the part of this curve that increases (A) and then using the duration at max internal score (B).
My concern for this technique is that it is not a precise prediction at all. At Sid or Deity, with a x8 or x7 modified, it could be off by thousands of points simply by a misprediction about triangle for the A region. In the case of the 80k games, around 80% of the score came from the milking part after max population was reached. If max territory and max population is reached later, that percentage changes. Also, using domination limit, you have to know the average number of citizens that will be supported per tile of usable land, which is only 66% of the domination limit.
I made a script that predicts this sort of thing, but I have only tested it against a few HOF Huge Histographic games. I would need to test it more before saying that it is a good technique to predict score.