FPUs will be fine from China. The problem with some Chinese sellers is that some will take older versions of a chip, or different versions of a chip, and relabel them as something newer / with more features. For instance, I ordered a late mask Freescale m68040, only to find it was an older and relabeled EC040 when I got it.

Regarding m68881 and m68882 chips, there are no older ones to worry about.

Any socket which can take one can take the other, but the m68882 will be a little faster than the m68881 at the same clock speed, so that's usually preferable. No clue whether it'd speed up SimCity, but it's worth a try.