I actually tried K ENB at 4K with some tweaks of course(otherwise it's impossbile to run), even my pitiful 280X Toxic managed to give me around 10-18 FPS in outdoors. I'm assuming these badboys can handle 4K quite well, especially with SLI. And also I made some changes in my ini files, draw distance was huge, uGrids was 9 and etc... Even then managed to get around 15FPS at Whiterun outdoors. A new era for Skyrim has begun :P