Having the same problem on a Radeon HD 5870, so not a nVidia problem. Ran great before 1.4.
It's terrible during space missions, as well. Ship chops around like a wave runner.
Also getting anomalous glitches, including a persistent white box which covers the top-left quadrant of my screen every time I log out (on an unrelated note, every time I log out, it takes me to the Create New Character screen..).