1920x1080 is the best resolution, but does playing on 1600x1200 with med/high settings look much worse? Or run any better?

I used default and It put me at 1920x1080 at medium and doesn't run the smoothest, is this a processor problem?

You might want to post your PC specs if you want help optimizing your settings.

If your monitor's native resolution is 1920x1080, you should play on that. Playing 1280x1024 on a monitor that's native resolution is 1280x1024 looks MUCH better than playing 1280x1024 on a monitor's that's native resolution is 1680x1050 for example.

Intel core I7 q720
Gs 7900 - I know it's not the best.
I have enough ram. Is that enough ?

My native resolution is 1920x1080 so thanks for the help on that.

Any other ideas?

a gs 7900 will struggle. leave the resolution and tweak things like draw distance, shadows, AA and such.