I am going to somewhat agree with Gumption's recommendation but suggest the 2GB version. http://www.newegg.com/Product/Product.aspx?Item=N82E16814161372
For the price difference I simply don't see the point in going with the 1GB.
It's a 20 dollar difference when counting the shipping prices. Plus the 2GB version comes with a Dirt 3 free.
In the end its $70 over budget but I am much more confident that a 6950 2GB will be able to handle the game maxed out. I really don't see the game being maxed out on anything less. If this is out of your range then you are going to have to settle on a lesser card and not max the game out. If that is the case then any of the previously suggested cards will do fine.