I played a few games around 250, once I managed 246. I definately could have gotten a couple turns better by polishing the strategy, but probably not below 240.
I can think of only 2 ways to get way better - either to get very lucky with cultural CS's quests and get several of them allied very early or get continents connected by shallow water to find all 7 civs before astronomy (which I had only once out of about 11 tries or something and in that game I got double DoWed so no luck either).