I put both:
fdefaultfov=85
fDefaultWorldFOV=85
in both the [General] and [Display] sections
in both the Skyrim.ini and SkyrimPrefs.ini files in the C:\Users\\Documents\My Games\Skyrim folder.
Seems to work...
Yess, that seems to work!
So in other words.. I pasted 4 times :
fdefaultfov=90
fDefaultWorldFOV=90
in..
Skyrim.ini / [General]
Skyrim.ini / [Display]
SkyrimPrefs.ini / [General]
SkyrimPrefs.ini / [Display]
no need for extra steps.