I believe Azaltan is correct here. With everything maxed out + Beths texure pack 1.5 vram would be stressed. A GTX590 or SLI'd 580's (3gb vram) will run you at 60fps inside, outside, upside down, any which way. I have 2 580's about 55 mods installed and get 60fps constant on steps at Whiterun. On steps at Markarth ouside Thanes home, I can find a couple of spots where it dips to 55-56 fps.