Oyster Bay passed the 100k population mark today, and I had to do a good bit of tweaking to the layout in order to accomplish that. (Going around and upgrading any medium density zoning to high density, changing any undeveloped zones to one of the other two types, adding in a park here or there, re-arranging streets.) I'm not sure if I'm going to be able to get much above 100k or not, there's not much room left to tweak the city, unless I switch over to a subway system instead of trains (hmm...). Since Oyster Bay imports all of its electricity and exports all of its garbage, air and water pollution are very low, but I'm not sure yet how that impacts all the aspects of growing a city (other then less is better).