Originally posted by ElephantU
Two big issues with doing this in a normal game: the terrain is ultra-perfect, and the AI was "goaded" to grow unusually large and build key improvements. Usually I am connecting to a size 8 AI city, rarely do they go up to size 12 - and even rarer to fund them close enough to your SSC. My last game there were only 2 size 12 AI cities in the whole game by the end, and I was playing OCC.
The biggest contributor to high trade routes is taking the chance on keeping an AI city close enough to get the RR bonus. Most players wipe their starting continent clean of AI and defend it religiously. Worth thinking about...
Agreed. I'm doing this for my own entertainment/research/theoretical pondering.
I did learn a few things...
- There is no limit to trade route payouts other than the limits of the trade in the city. Because the value tends to jump periodically (as the trade in the AI city grows), there were times I thought there might be some sort of cap. Turns out I think you just need to increase total trade in large increments to get a bump in the value of the routes.
- The AI will eventually build Superhighways once in a while, but usually too late to matter (I was starting to wonder if they ever build it)
- The AI is incredibly stupid (even more than I thought) when it comes to engineers/settlers. On a completely improved island with no free land suitable to settle and a completed sewer system, a size 12 city will crank out 2-3 more settlers, just because it can.

This amplifies your point about the cities rarely growing past size 12. The AI had nowhere to go, had a sewer, and a food surplus, but god help them if they didn't have 4 engineers running around doing nothing.
This stuff is more apt to apply in OCC games than normal games because of the need for the RR Trading partner, but the principles learned could apply to other situations as well (just at a lower bonus level on the trade routes).
In Non-OCC games I think you are better off making routes with a well placed, well developed domestic city where you can focus your efforts on growth, maximized trade and appropriate improvements in both cities. You give up the foreign doubler, but you are more likely able to get the RR bonus and can probably make up the rest with the extra trade and 2 superhighways at least late in the game.
I also think the value of rivers has been underestimated in the placement of an SSC. They provide the equivalent of roads immediately, they provide a bonus arrow for the road once bridge building is discovered, and because river squares have 4 trade instead of 3, the 50% superhighway bonus gives 2 extra instead of 1. Add to this the ability to get trade from high-sheild squares. I honestly think I'd rather have a 0-special, 10 river city site, than say, 2-3 wine and no rivers.