The only problem is that if you build a lot of cities every 4 squares apart, you lose a lot of potential food as that 4 food grassland gives only 2 food with a city on it. I found combining large (25+) cities with a smaller one of size 12 managed to keep both happy pretty easily in heavily corrupt areas. Don't know if that's the best method, but it's working ok. I suspect that the differences between these methods are pretty minor anyway, and mostly a matter of playing style
As for a 10,000+ score... I don't think we'll see it. I believe that the absolute limit will be around 8000 on this map. Why? Well, for one thing this isn't a HOF game, so there won't be reloading on combat to get optimal results. It is also large for another thing. I've been comparing this game to GOTM#2, also on large map with the starting point separated from the main continent - but on a more difficult monarch setting. In that game, Dirty Clint had the high score with 15,000 something. Since the score for Warlord is 1/2 of the score for monarch, we'd expect to see a score of about half that, or 7500 points. But the score should be higher, since Warlord is easier, right? Dirty Clint's save file isn't included (he submitted a few days late), but when looking at SirPleb's (the 2nd highest scorer) I saw that he conquered the world quite early, before 1800AD. After that it was all milking the game.
Now let's assume that Dirty Clint conquered the world earlier, say by 1700 and built up score after that. With the difficulties involved in transporting troops, across an ocean before researching at least to astronomy for caravels, I don't think anyone could get the requisite land needed before 1200AD. Maybe someone will surprise me, but 1000-1200AD seems the absolute earliest anyone could both research up to the ships needed and launch an invasion force capable of beating either England/Germany or China/Zululand/Japan. That's only approximately 150 turns before the conquest in GOTM#2, which is not a big enough difference to offset the drop in score from difficulty.
Furthermore, remember that the cities that GOTM#2 winners like Dirty Clint and SirPleb were taking from the AI were already completely railroaded and large in size. Since tech moves slower and the AIs are worse on warlord, those conquering land will have to build it up themselves after taking it. In other words, instead of taking size 15 cities, in GOTM6 you get size 2 cities, and have to wait for them to grow up to that size. Not to mention having to wait to research techs like Steam Power and Sanitation yourself.
One final note is that the GOTM2 was played with domination victory DISABLED. That means those scores were accumulated with the entire map full of cities. It should be much harder just to get 1/2 the winning score without going over the domination limit in GOTM6. Think of how much higher your score would be if you could put cities over the WHOLE map!
Now this is just speculation; maybe someone out there conquered the world in 500AD and built his way to railroads and hospitals by 1000AD and will blow us out of the water. But I think that 8000 is a good target range for the winning score; the separate continent, slow pace of tech, and domination threshold to be avoided make getting to 10000 points very unlikely in my mind.
)
Fortunately the Japanese and Chinese went to war and collapsed into monarchy; I have already converted one city using propaganda and hope to get a few more; another city will fall on culture any turn now. 
) but I'm still moving at a pretty good tech pace, should reach modern age around 1800. Having so many 25+ size cities without mass transportation kind of sucks though with global warming (the fact that I am cutting down every forest and jungle tile in my territory doesn't make things better either! 
(yeah, right)
