Bibor
Doomsday Machine
I usually shoot for cities of about ~10 population. After that the growth slows way down, so I feel like it's more efficient to just start a new city. Plus, the returns are better for the basic buildings than for the more advanced ones, so I'd rather have a lot of basic buildings than a few advanced ones.
Not entirely true. A size 15-pop city will almost always be better than two 10-size cities.
It is completely relevant. You mentioned how many turns it takes you to build buildings/units.
And the difficulty you played in Civ4 is completely irrelevant. It's about how good your argument is. How would you like it if I said I played on Immortal/Deity, so you should listen to me when I say that tile yields are low?
No, I wouldn't listen. Your armies are stronger by 33% by default (I have yet to see a great general fielded by the AI), and yet another 50% due to the simple fact that the AI can't handle any unit but the basic infantry. Even if the AI gets a 40% production bonus, they loose 20 artillery to your 1 or 10 archers to your 2.
And as for CIV4 deity, from what I read it was never about production or commerce but about bulbing/techtrading abuse and the whip. At least as far as USUN's, TMIT's and DMOC's games are concerned.