In cities using the Standard graphics options, I get anywhere from 40-50 and 30-40 if I'm running on maximum.

My frames seem very jumpy and unstable.

My specs are:

GPU: GTX 670
CPU: i5-3570k @ 3.4 ghz
PSU: 750W
RAM: 8 GB

Is the game somewhat unoptimized?

I haven't read any complaints from others on this subject.