Running at 1366x768 doesn't pose much of a problem for the GPUs we tested -- even the GTX 750 Ti was good for 57fps. The R9 265 was even faster rendering an average of 65fps, while the R9 285 rested easy with 81fps. Beyond that the results aren't worth talking about as 80fps+ is more than enough to deliver perfectly smooth gameplay.
Jumping to 1080p shows a rapid decline in performance as the GTX 750 Ti drops to 33fps and the R9 265 39fps. This time the R9 285 along with the GTX 760 and GTX 960 all averaged below 60fps while it took the GTX 770 and R9 280X to break 60fps.
Gaming at 2560x1600 will require some GPU horsepower, as not even the GTX 980 could achieve an average of 60fps. That said, keep in mind that we are testing with the ultra preset which applies 4xMSAA. At this resolution, you should be able to get away with a less extreme anti-aliasing mode.