No 1st spoiler.
I was feeling frisky and chose the challenger save. 1838 AD (t 289) Domination. Score about 35 000 (would've been just short of 50 000 if the difficulty was taken into account

).
Settled 1NW of the settler for two food resources. In retrospect, this probably wasn't very useful, since most of the time I was using only one. Hatty expanded eastwards and managed to put a city on the "chokepoint" between our continents, but I secured the land on my side and got to 6 cities which I decided to use as a base for knight push.
I went on to build the Colossus for 3 reasons:
- Financial trait
- Lots of water tiles
- MC is on the Guilds techpath anyway
After dealing with Hatty, it was a fairly straightforward game: I put a few more cities on my newly conquered continent (and took a barb city on the SE island with some leftover knights), teched Military Tradition (Libbed it, actually), Gunpowder and Astronomy. Then built some Galleons and a bunch of cavalry.
The first victim was Cyrus as he was the most advanced (and by that I mean "the only other guy with gunpowder"). Muskets worked against cavalry as much as you'd expect (except the one time he took a city back at <2% odds

) and he was dead soon.
While this was going on, I teched to communism and adopted State Property to avoid being bankrupted by the Persian cities. After this, I shut down my research for the rest of the game and ran the culture slider at 40-50%. This served two purposes: quick border pops in captured cities and countering war/whip anger on the home continent. It also caused a couple of cities to flip to me at the very end of the game.
After Cyrus, it was Roosy's turn (more island-hopping, yay). He fell quickly as he wasn't even close to rifling and he had lost some cities to Nappy earlier. He'd also been at war with Toku at some point. Come to think of it, he really got the short end of the stick when it comes to neighbours.
Nappy was the next natural target because he was the 2nd biggest civ and my forces were already on his doorstep. He did have 10 cities in the mainland and a fair amount of units, but still nothing better than musketeers and pikes, so I steamrolled over him, too. I was preparing to declare on Toku, but it wasn't necessary because the French cities pushed me over the Dom limit when they came out of revolt.
In the end, there was eleven and a half hours on the game clock, which is pretty long for me (my games normally last about 6h). Undoubtedly, the fact that this was a water map played a part in it. When the war machine started rolling, I neglected my empire pretty badly, leaving it mostly to the AI's hands. I just don't have the patience to micro-manage big empires (I can barely do small ones) and I'm sure that's going to show on the scoreboard. It's too bad you can't take vassals in vanilla; this game might have been over a lot sooner.