I originally thought that the GOTM encouraged really milking the game for a long time too, but I now realize the flaw in my logic - wltkd. If you finish your game extremely early, exploiting the fact that you can triple your score within a matter of 10 or 15 turns, you can attain enormous scores. I am unsure whether an early landing or conquest is better - I usually end up conquering the world whenever possible anyway, just because it allows for more points with relatively little investment ( a few tanks easily handle the horribly slow teching computers). The bottom line though, if you ever want to attain a score well above 500 you better plan on an early finish, with as much planning as possible to have all of your cities celebrate to their maximum at the same time, and the same year you end the game.
FYI, the growth of your civ may be constant by percentage, but this isn't really a useful piece of information. What I found to be the best way to maximize gotm score was to compare when exactly it would be most ideal to begin global celebration to attain the largest score by the time all cities reached the end of their festivities. The exact date is always dependent on how big the map is, and how much easily useable land there is. The ideal, which you would milk the longest, would be many small islands with grassland squares and alot of ocean for each city, since this requires minimal improvement effort to celebrate (a harbor and sometimes a marketplace/courthouse is about all you ever need with 30% luxury). Even under these ideal conditions, it would still seem to behoove a player to finish very early - no later than 1000 AD if possible.
The idea of having 250 size 40 cities isn't a practical conclusion, because it is very likely that these cities will be growing to a size 40~ at very different rates. By the time you place your last city, you could boost it to size 8 right away, but it would still require 33~ turns to grow to 40, assuming you can pull off a nonstop growth. By that time, it is very likely that most of your civ would be already at its max pop, and you would be losing points in the process of growing your last city. The true solution seems to be that you want to build as many settlers as possible, constantly expanding to all places, then celebrate them all together at some ideal point which would vary from game to game.