Sim City 4 still needs enough processing power on a single core to run smoothly, though. It will crash to desktop every time it starts to use more than one core. Running it on a multi-core/multi-CPU system, it's a matter of when it'll crash, not if it'll crash.
I'm curious as to what you're running now and if you've chosen to limit the game to a single core.
I've actually had a game crash my entire system (actually my current system) once because there was more memory available to the system than the game could actually recognize. The game was barely even 10 years old at the time, too, so it was presumably a 32-bit game, so emulation should have generally played nice!