Ok, here is the quick and dirty T72 Great Wall in Canal City test.
The results are very promising.
New Capital Worker chops 10

forest 1E of Wheat T63, the same turn as 2-pop whip of Granary.

(Worker can head back to capital to chop/cottage/build road starting T64)
T63 capital puts 73
into Great Wall from overflow on Chariot whip T62.
T64, Canal City puts 82

into Great Wall thanks to 10

chop near wheat + 30

overflow from Granary whip
T70, Canal City puts 20

into Great Wall thanks to overflow from Lighthouse whip
T72, Canal City can 2-pop whip The Great Wall complete if AI hasn't built wonder yet. (Test Game Mansa completed Great Wall T72

)
T73, Fail gold from Silver, Whales, Profit lands from Great Wall
T74, Fail gold from Cow + Science city lands from Great Wall
There are 6 more turns that capital, Cow City, and other cities can put chops and overflow into Great Wall.
T65, T66, T67, T68, T69, T71
Silver City can probably chop outside the BFC for 1 turn to get Great Wall fail gold.
This will help out our tech rate a lot on T73.
Workers can furiously chop into Stonehenge in Cow City, then Great Wall.
Dun stone trick road to deer does not need to be finished until around T78 or so.
**Edit**
Will work on a concrete plan to get to Oracle tonight, so no further results from me for 12 hours.
Looks like Cow City can chop 1 time into Stonehenge T64, and then x3 chop T69 into Great Wall which almost completes it in 1 turn

That leaves uhh, 1 forest for Mids.
T55 Real Game screenshots
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