I have play COD6: Modern Warfare 2, and it's awesome like version before.
If you want to have both performance and graphic beauty, follow this settings for 9300m gs card only.
I get average 35 fps for my 512 MB 9300m GS with these settings:
Resolution - 800 x 600 (If want higher resolution, should disable AA).
Anti-aliasing - 4x
Texture - Automatic / all Extra (put medium or high for 256MB 9300m GS).
Additional info : 9300m GS almost same as 6600GT, which is minimum system requirement for COD 4, 5 and 6, but 9300m GS better at handling newer game.