Factorio is my recommendation. That game is optimized insanely well, and it's easily one of my favorite of all time.

I'd also add Dwarf Fortress. Eventually it'll slow down (it does for everyone), but you can set limits and choose settings that allow it to run well on your system almost no matter what it is. You may need to choose a pocket world and limit the number of dwarves below default, but it'll work.