Well, yeah, I'm going to probably play the "take all cities from an AI, milk them for workers, then abandon them all" game. I'll probably just keep all the starting continent cities until Tanks come about(which seems to happen around 1400 or so on Diety Continents). Then I'll go all out with tanks/transports, flatten the other continent down to one city, surround it with tons and tons of troops(so they can't get any settlers out), then abandon most of the cities on my continent, until I've got two cores, each at OCN/2 cities, one around the Palace and one around the FP. Then I'll go all-out research until I've hit the last tech(for Strategic Missile Defense or whatever it is). After that(this shouldn't happen until at least 1800 AD by my calculations) I'll see how much CPT I'll need to hit 2048-49 for a victory date, and sell various buildings to reach that goal.
OCN on a standard map is 16, right? Ok, so that means I'll have 16 cities around from 1400ish to 2049, which is a very long time in game turns (at least 250, probably more), or nearly half of the game. I'll probably abandon all but a core of 4-5 after I get the last tech.
I'll actually see what happens after I finish off my continent, see what the tech situation is, and how many more wonders/improvements I'll need. Then I'll work on reducing the other continents, and abandon all but the capital once I've (1) finished off the AIs and (2) got enough wonders to win. (Will edit with more later.)
Ok, here's the basic point I'm getting at: I'm not exactly a stellar Diety player yet (1-6 in my test games, and none of them 20k). So I'm probably going to need all the cities I can get to cripple the AIs to the point where they can't get Space Race victory. But, if I can spend 200+ turns with just a core or 1-2 cities(I'll need 2 if I want to be able to use the Palace as a prebuild in the 20k city) then the end score will probably be pretty low. I might also need at least one city on the other continent to ship lux/resources across from, even with colonies the goods can't get across the ocean without a harbor/airport city. But, other than that, I can probably count on a low score even with a good hold on my own continent for the majority of the researching portion of the game. (Also, once my 20k city hits 10,000, there's room for some 0-culture cities to be put in there for production/gold/UNIT SUPPORT purposes without expanding the borders.)