Whoops, 4 posts in a row, sorry about that...
Well, you know how it goes, you wake up one morning and you have a completely different idea on what to do. How about ditching the whole GLH plan away? :suicide:
If you look at our opponents' graphs you'll see that Ducks have almost 300 in score at T80. Other teams are climbing high as well. Our score by that time, with plan I or Y or something similar, will be around 215. This means that they are not going for the GLH, at least not an early one.
GLH is 200 hammers. With +50% Imperialistic, that's 300 settler hammers. This is very hard for me to evaluate, but what about building 3 settlers instead? I considered it before and dismissed it. This requires more thought, especially since we have other teams expanding more rapidly.
GLH value highly depends on the map. If we're stuck to our own trade routes, that will be 2

from each city after the 4th city is built. (each city will have 3 trade routes, 2 from GLH) Let's say we build 6 cities with the GLH, but manage 9 without it. 6 cities would yield 12 GLH

each turn. Surely, 3 more cities would top that! (in hammers or whatever) The problem is that we don't know, maybe there are islands we could settle and we're not land limited.
I've had a look on that Dynamic's HoF game. 252 turns, 1710 AD. He took a land only map, to maximize the hammers for space parts. He got 23 cities, all peacefully! It was an odd map, with him being in the corner and some large mountain passes blocking the land. At the end, he was pushing 4k beakers/turn with a combination of some central city towns and SP workshops elsewhere. 16 great people were generated, with Communism as Liberalism free tech. Also, he got the Pyramids at around 1AD that helped him with research.
I don't see anybody beating that game with this scenario. It does put the emphasis on gaining land cities, though. We know there's at least one land neighbor around. Judging by the tests, the AI will build a lot of archers, making any early warring very difficult. Maybe we'll do some harassing, but real conquering will probably come in the Renaissance. So, on one hand we could gain by more early settling, but on the other GLH could help us get to Renaissance sooner to start the war more quickly.

How does one determine this so early?
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The alternative plan would be to do the beeline Writing->Alphabet->Currency and to maximize early settling. Some of our cities would build

to speed up research to Currency, switching to wealth to increase the gain from capital Academy and capital cottages. I've had games like that on immortal, it's a useful approach with few river tiles for cottages. (I prefer not to build cottages on regular grassland when playing with non financial civ.) Early Currency also brings 1 additional trade route, half of the GLH effect.
But how do we decide to dismiss the GLH? Any ideas on how to evaluate this? (Other than just going along with the Ducks!

) Even if we do, that's an all deity team there, how wrong could it be?

I'm really leaning towards that Alpha->Currency idea here. We have health issues and we have to expand. I think that's a better plan than going for Monarchy and vertical growth at this point, building the GLH or not.