How does the game run for you on these settings? For me (with a similar system) I would find your settings a little ambitious. I might turn building detail down to medium but up buildings amount to unlimited. I leave the Catalyst settings as default, for me AA does not seem to make much difference above 2x. I also find it beneficial to reduce the resolution and refresh rate in order to turn the video settings up.
On line I tend to turn trees off to lessen the occurance of the missing sound bug in mp, this is not always necessary though and whilst the trees are a special fly-through-without-consequence variety they do add to the eye candy for me.
Good luck
