If you edit “\res\models\model\asset\chimney_XXX” files and remove all the particle emitters, then newly created buildings will not emit smoke from their chimneys. This yields quite significant speed-bump when viewing cities.
I tried this and I’ve started a new game on 1950, just to see what happens. I’ve got about 20 lines so far, and it’s hard to say for sure (my pop is lower) but I feel like it’s faster. I wish there was a way to test a game with and without it, but you’d have to wait for the buildings to rebuild or something right?