It seems like City + useful terminals might be a good counter to IGG, though, since you're sure to have the cities activate.
I haven't actually played this, though, and searching councilroom for top players who've played games with IGG/City doesn't yield anything useful.
Simulator hates pure City v IGG (90%+ win rate for IGG player, and that's without the possibility of him ending the game on Cities), and adding something like Smithy or Salvager doesn't really help much. Is this another case of Trade Route/Crossroads (seems like a good idea in theory but just doesn't work in practice)?