I would love to know how you guys get such good performance. I gave up on this game several months ago (much to my dismay) because at a population of 40,000 full game speed is NO BETTER than the minimum game speed. A full day takes 13 seconds at max speed. Here are my specs:
i7-4770 (@3.4GHz)
16GB RAM
Radeon R9 390X with 8 GB RAM.
I am running several mods... however I am very experienced with modding and NO set of mods in any game that I have ever played or modded has ever quartered the game speed unless they were very graphics intensive. The graphics card is new since my last play back in October but it has only affected the smoothness of graphics. Graphics are amazing. However it has not improved simulation performance AT ALL. All city simulators I have played previously don't start taking performance hits until the population is MUCH MUCH higher (a couple hundred thousand or so).
Remember this is an agent based simulator and cims needs to get from point A to point B in a timely manner. Your issue are two-fold, you use mods which increase the load on the CPU. I've seen Traffic++ alone double the load by cutting my FPS in half, plus poor city layout increasing traffic agents and other cim agents making you lose even more computer resources. early game it's usually imports/exports and not enough highways to cims to their destinations on time.
currently, the latest patch has issues with bike lanes and surely other issues yet to be determined. so if currently it has gotten worse, it may take some time to find all the bugs. There should be a patch out soon.
You sound like your other games aren't agent based simulators as they use lots of CPU and little graphics. Mods for this game are usually AI behavior people aren't happy with and modify it and it uses up even more resources. Your graphics card is way past the recommended and I can't ever see any reason your card would bog down. so no, your graphics card has zero performance affects on this game as it is mostly all CPU based. Tracking agents (CPU) vs. drawing agents(GPU).
Performance hit won't occur until you start saturating the agent limits. The game has built in limits, with the new patch you're experiencing these limits earlier than normal if you haven't played since October. Once the patch is out it should get smoother. Hopefully once patch is all that will be needed and you can be returned to normal play.
You can try upgrading (down grading) bike lane roads to normal roads. Bike lanes seem to be a major issue. Just don't over write your saved game if you choose to continue playing without bike lanes so, you can go back to your old game when the patch is finished completely.
I think a normal day takes around 8 seconds, although my new game with Snowfall takes 3-4 seconds. Maybe it just depends on your CPU loads. I don't use any mods except unlock 25-tiles which you can unsubscribe as soon as all 25-tiles are unlocked. But the key to best performance is no mods or assets. assets have a much smaller impact, but can slow down in some instances. especial when they are more than a cosmetic mod.
