Signed up just to chime in that I have the exact same problem. I go from a stable 50 to slideshow fps in random locations when looking at random directions. I assumed it was DynDOLOD or something. In a make shift test, I jumped around a giant boulder, where my fps tanked and the drop only happened when I looked at boulder from a specific side. The boulder/rock wall was slightly bigger than my character and would block the distant view in first person. On the other side of this boulder, my framerate was fine whether I looked toward the distance or at the boulder. My game only turned into a slideshow when I was standing in this very specific spot and looked in a very specific direction. Now I should say, I've added several additional mods that change gameplay and add wandering generic NPCs and such. So this could be a weird script issue. I also have zero knowledge about Skyrim stability, so I'm just guessing and saying what happened. Just echoing a weird issue.
