You can turtle your way to a reasonably fast science win (~T200) with as little as 12 cities. The GP involved put a hard limit on how long the game will take, as Sagan along with a couple chops will end the game. If you go all out conquest dom wins are easily achievable prior to T200. I don't play culture or religion, but posts in the forum indicate those games are easily winnable prior to T200 even with a modest number of cities. You'll have the number of cities required no later than T100, and often much faster. In a game I played yesterday I had 15 cities at T60. From there so long as you don't make any egregious errors victory by T200 is easily achievable. The late game feels empty because the game is already supposed to be over.