I'm planning on buying a new GPU in a few weeks and I remember reading last year that the game had some trouble with AMD cards due to the older OpenGL drivers it uses.

So, if I get a new AMD GPU, specifically an HD 6850, will the game run better or worse?, right now, the game seems to run pretty decently, it runs at ~20 fps when there's a lot going on at once, with everything maxed out and with antialiasing set to 4x and a resolution of 1440x900, I'm using a GeForce 9600 GT.