Ultra is the best setting. It draws all the scenery around you 360°, so when you look around there is no loading in of textures, trees, buildings, etc. It is all loaded up in your memory, so its silky smooth gameplay.
Having an older CPU (i7-4770k), I had horrible stuttering when panning the camera. CPU would jump up to 100% usage while trying to draw all of the scenery every time i turned the camera. So, having it all loaded up ahead and banked in memory has dramatically improved performance for me. Its pretty much how it used to be pre SU5.