I think, that this target on such a resolution wouldn't be possible. It depends on vram bigger 2 gb (better 2,5 or 3 gb) to reduce stutters from texture loading), but it also depends on the rest of the system.
1.) The game uses streaming engine and so, the landscape loads frim hdd at some point. So an SSD would be helpful to reduce stutters as well.
2.) At sone point the CPU gets the bottleneck and this could happen here, too. The game do not use multicore very well (just 2 cores effectively, if I am right?)
-> These 2 points are main focus. Later on it is also depending on small things like normal ram, the vram interface on the graphics card (which is quite slow for a top edge card like the 680 -> ati has a larger interface), etc.
I personally say: A high resolution and a streaming engine game is ATI strength. High vram, good interface and better performance on higher resolution beginning at your intended resolution upwards.
So, just to throw it in this thread: Did you also have an eye on hd7970 card?
Opinions and corrections appreciated. I try to learn more and more on this.
Last word: I think, that constant 60+fps is hardly reachable with current situation with highest settings.