You should be fine at Ultra. I ran Skyrim on my GTX 580, which is right about even with the GTX 660 Ti. FPS ~60, even after enabling all the quality tweaks I could find. Be sure to force Ambient Occlusion through the Nvidia control panel for the best visual quality
Ultra settings, 4x AA:
http://www.techpowerup.com/reviews/Gigabyte/GTX_660_OC/22.html