Cities Skylines sees a fairly decent improvement going to the 3D cache chips from AMD (17% speedup here for the 5800x3D). Whats your ability to increase the budget to go for a 7800X3D look like? If this is a genre of game you like and you want to hold off as long as possible between upgrades, it might be worth springing the extra. The difference the 3D cache provides in some games is rather extraordinary. City builders, automation, and similar games tend to benefit the most. AAA games tend to benefit the least (some with effectively no gain).
A 7600X should be more than capable of handling the game though. So it’s not a question of need but if it’s worth it to you.
You do not want 4800 CL40 RAM though, that’s too slow. I’d strongly recommend going for 32GB of RAM as well; 16GB can be gobbled up quickly, especially if you want to use mods in Cities Skylines.
Going up even to DDR5-6000 is not much of a price increase. I’d suggest 6000 and something in the range of CL36-CL40. There’s a lot of 32GB kits in those specs in the ~$90 range. I would not build a gaming system today with 16GB of RAM.
Do you have data on that? A modern nuclear power plant is going to be in the 500-1000+ MW range. I have a hard time imagining that even operating at half capacity that they do not offset the carbon used for concrete within a relatively short order. But if that is in fact the case I’d love to see data saying so, so that I can correct my thinking.