I can only play on medium with some performance enhancers. If you ever need to use them, I'll link to them for ya right now.
http://skyrim.nexusmods.com/mods/6387#
http://skyrim.nexusmods.com/mods/12801
Even if you can run on Ultra, still recommend using these since it makes the game so much more smoother in controls. The controls were extremely laggy for me before I used these svckers.
Here is also a bunch of other mods that make the game look a tad better without sacrificing performance or changing gameplay
http://skyrim.nexusmods.com/mods/679
Bump Roads Vanilla V1
Enhanced Distant Terrain (slight frame rate drop, although not much)
http://skyrim.nexusmods.com/mods/2356
Real Glaciers V2
Realistic lighting with customization (note, this makes it dark enough in caves that you will actually need a torch, so it technically changes gameplay, just letting u know)
Realistic Water Textures
You will have to look these up on the Nexus