I had the exact same problem. Leaving dragonsreach castle into whiterun gave me an infinite load screen. I even removed all my mods to see if one was causing it. I still had the problem, so I went and loaded a save I had on another character from before I started modding and STILL had the problem. So I started looking around the webs to see if anyone else had the same problem and I came across this thread. I have to thank you about for your comment on the ini file. I had added the zoomable map tweak to C:\Users\*username*\Documents\My Games\Skyrim\Skyrim.ini and you made me rememeber it. (Thats windows 7, I don't know where it is in any other OS) I went and removed it and now I can load again. I have all settings in the launcher set to ultimate except the shadows which are on high. I hope this is helpful to you, but if this was the same ini as you said you rebuilt (and therefore isn't helpful to you) hopefully this'll at least help some people.