I hope to improve performance in the coming weeks but a little performance drop will always be unavoidable. And as cities get bigger, performance gets worse.
You don't need to build anything to affect performance. All checks are run in case you did build something.

Same Problem here, at 60 k citizens performance drops by about 75% just by enabling the Mod.
CPU isn't affected, stay at about 30-40% on my 4 Core/8 Threads Core i7 @ 4 GHz.
Looks like calculations are limited to one thread, multithreading support would bring a huge performance bump on most systems :-)

The CPU load doesn't need to increase for you to experience a performance drop and I don't see how my mod could affect rendering times.
More than that, what causes performance problems is the custom pathfinding which is run by the CPU and it's multithreaded. :)

Maybe i wasnt clear with my statement. Whats dropping is game speed on max speed settings.
I dont think rendering times are the problem, its most probably pathfinding as you stated. I would expect CPU load going up if pathfinding is the limiting factor and implementation is multithreaded?

The game reduces the max speed as the city grows... can't find the link but there was an interview with one of the CO devs and they mentioned that there are a few stages where the game shifts in to a different mode as the city grows. One of them was 60k or 80k pop (can't remember which) and the other was something like 200k pop.

That being said, anything that eats CPU will make matters worse; the next T++ release will solve a lot of those issues as it's waaay faster than the current version.