I have the exact same issue right now (the extreme framerate-drops). thought it was because I installed to many mods and messed up my game in general. So I reinstalled skyrim, started a new game without mods and got the exact same issue. I used to be able to play skyrim at more than ultra settings with stable 60 fps, with my enb 35-50. Now I have 60 fps in most places, but when I´m looking at certain far-away-places my fps drops to 1. When I´m turning around I get 60 again :/ .Doesn´t happen indoors for me as well. My guess is that it is some kind of LOD problem, because when I turned down the sight range it got better for some places. So you might want to try that. Still my game is unplayable in some locations :( English is not my native language, but I hope you can understand what I´m saying :p