you have 6g so I can't believe you had to turn off areo.

I run several copies of wow and don't need to turn stuff off.
I set my video settings for performance and turn off the fade-in junk but still.
maybe you need a faster video card.

and limiting the video card to 512M instead of using some of that left over memory will probably only slow down your system instead of speed it up.
Just because the video card can use that much memory doesn't mean it is.