Keep in mind, this game is not currently running full screen. Recommending people lower end graphics cards saying "I ran it full ultra with this card" is a little quick on the draw. Lacking full screen mode doesn't allow for hardware enhancements such as antialiasing, anisotropic filtering, and a whole slew of other graphical enhancements.
Until it is true full screen, we will not know what cards will run everything jacked up to full. For instance at 2560x1440, my 6990 crossfire struggled in certain areas dipping below 25fps (crossfire does not work). This was with no antialiasing (the in game setting does NOT work), and no enhanced filtering of any kind.
I guarantee you when this game gets a true full screen, it will be MUCH harder on your system than it currently is. Sure, you can just play it with the settings that you currently do since AA isn't even functioning, but then you aren't actually playing with full detail.
If you think the game looks good now, just wait until real full screen hits, and your hardware can take over.