And here we are at 1500 AD. The Corporation Advisor, showing the scoring tally:
21 cities with the corporation, for 42 points. And 80 culture per city is exactly 40 seafood resources, for 40 points.
Despite 
strictly following the variant rule, I still managed to get my economy into a little bit of a crash. What I did was settle all the cities and expand the corporation, BUT I held off on all the Fishing Nets to delay increasing the corporate costs. The Work Boats just stayed in place until all the cities were settled and incorporated while following the 50% economy rule. Then each new Fishing Boat cost me about 20 per turn in corporate maintenance, for over 300 total!
Still though, even this economy was still making over 400 beakers per turn, and in the black at 30% research, which would quickly improve as the new cities grew up to size and whipped courthouses and libraries and banks and well everything.
And, honestly, the rest of this game wasn't very interesting. I'd already claimed all the available sushi sites, and declaring any war clearly couldn't recover the loss of double score.
My victory type from here was definitely space. In *game* terms, culture would clearly be easier, with a free 80 per turn in each city already. But I'm not well set up for culture in *competitive* terms, with very little religious access and planning. Rather, I think I'm better set up for space in competitive terms. Having expanded this far this quickly, I should have a strong economy to reach Alpha Centauri first. Also, I'd like a no-pressure practice run through the BTS space race in case I choose this option in an upcoming competitive game.
(I later looked at the scoring results and confirmed that my intuition was correct. Swiss Pauli recorded culture in 1764 AD, which I definitely couldn't beat. But the earliest space win was LKendter in 1968 AD, fairly late.)
Anyway, I got Taj Mahal while researching Replaceable Parts, and slinged Liberalism into Assembly Line, and used the golden age to do this:
Free Religion was a pretty clear call over Org Rel by now, with research clearly the long pole to space and religion a liability at the diplomacy table. But why Nationhood? Well, it's actually the most productive Legal civic at the moment! Bureaucracy has long outlived its usefulness, with the high civic upkeep easily outweighing the commerce at my capital. And Free Speech isn't too useful yet since I don't have a lot of towns. So Nationhood with no upkeep actually comes out ahead, especially adding the Barracks happiness.
Also, it lets me do some sanity-saving. With Assembly Line, I could draft infantry, and did in each of my cities besides the homeland. With absurd Sushi growth, they'd never miss the population, and this saves me loads of tedious sailing and reinforcing each city. And since I was still in Hereditary Rule, the drafted units would mitigate their own anger.
Now, I don't know how Gilgamesh was doing it. THIS is the entire Sumerian empire: four size-8 cities. Gilgamesh is last in score, and his Creative and Protective aren't any sort of economic traits. Yet somehow, he's the game tech leader apart from myself. He's now at Friendly thanks to shared civics and no religion penalty, so even though Louis went WFYABTA, Gilgy is willing to trade me all sorts of techs. He traded me Steel for Education plus Rep Parts, and Sci Method for Liberalism plus Economics.
And at the end of the Golden Age, I revolted again to Representation + Free Speech. With the drafted units all over the place, I was now on top of the power graph by a significant margin. So I didn't need to hold onto HR for diplo reasons, or Nationhood for any more drafting.
So nothing happened. The AIs went to war with each other, but not with me. I had a few problems with happiness with the loss of HR and all the whipping, but Broadway + Eiffel + Rock N Roll fixed that.
Genghis spawned Qin Shi Huang as a colony vassal, which had no impact on anything.
My Ironworks city spawned a Great Engineer (a lucky break at 35% odds), who went for Mining Inc which I also spread around everywhere. It would directly make a profit, with each city costing about 10 gold in maintenance against +12 gold at the Wall Street HQ. And 10 extra hammers in each of my watery cities would go a long way towards completing all the builds. None of the other corps would help: Creative Constructions was inferior to Mining both in productivity and resource count; Cereal and Ethanol were directly out due to rice competition with Sushi; Jewelers isn't on the spaceship tech path; and Aluminum wasn't worth the effort with exactly two coals in the empire.
While all the other cities used the absurd Sushi growth to whip just about everything, my Heroic Epic city kept cranking out infantry constantly, to keep me on top of the power graph. It paused for a factory and coal plant, then resumed cranking Tanks, which give more power per hammer than Infantry (25000 for 180, compared to 16000 for 140.)
My economy did seriously grow through the roof, hitting over 5000 beakers per turn by the end of the game. Both Louis and Justinian researched Democracy, and since they wouldn't trade it, I had to burn half a turn of my own research (30%) to get it myself for Emancipation.
With the National Park / National Epic city in full swing, I fired a 2-man Golden Age to build SS Thrusters, and a 3-man GA shortly later with the GE at Fusion. I wouldn't make enough leaders for a 4-man Golden Age, so I sent two Great Merchants on trade missions for $3100 each to get several turns of 100% research rather than 70%.
In BTS, the correct late game tech path seems to be Ecology last, since that has the cheapest part with a resource doubler to boot. Before that, Genetics, with the second cheapest part. Make sure to get to Fusion soon, because there's two big Engines there.
I worried for a bit earlier that outracing my own cultural victory might be a problem, but it wasn't. Without any cathedrals, my third city only reached 20K culture by arrival time, still over 100 turns away from Legendary.
Space Race Victory in 1848 AD. (Turn 294, equivalent to Epic speed turn 441, which is 1851 AD.)
GNP graph, which shows the usual blowout, though about half that is Sushi culture. The drop at the end is from a neat Cristo Redentor trick: Schedule the last spaceship component to be built in your capital, and switch to Bureaucracy for the extra hammers once all the techs are complete. (Actually, this only speeded things by one turn, synchronizing the last component with two others.)
Wow, 322,000 normalized game points! OK, well, that's not comparable to any normal game. Population is the biggest component of score, and the Sushi corporation increased that by nearly 50%, with all my cities at size 30 instead of 20. And score also comes from the massive easy culture expansions claim land, and the resulting powerful economy from the corporation to speed the spaceship win.
So, endgame scoring:
40 points in 10 AD: 20 for cities + 20 for sushi
82 points in 1500 AD: 42 for cities + 40 for sushi
10 points for endgame Sushi resources: 42, which would be third place
15 points: Fastest Spaceship Victory
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179 x 2 = 358 points. That's ahead of Compromise's official winning total of 232, although IMO he should have gotten the doubled score. He took the diplo loss, but game victory was never listed as a requirement for the doubling. I expanded well (more 1500 AD resources than anyone else), but the better route to scoring really was Compromise's expansion to foreign cities, which I never did. Well, it's just a shadow game anyway. :)