I've a very annoying issue with Skyrim...sometimes, usually when I change from one cell to another (interior -> exterior, etc), my fps suddenly decides to drop into barely playable rates..
My system has been recently formatted, W7 reinstalled with minimum apps, no antivirus, disk defragmented just before downloading Skyrim, unnecesary W7 services disabled, W7 put in performance mode (without Aero and all that crap), W7 Update, sound and GPU drivers updated...seriously, I don't know what else to do... 
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Thing is that the game runs at fine fps most of the time...until it decides to drop them ??
CPU: Amd Phenom II x4 2,8 Ghz
GPU: Geforce GTX 560Ti - 1 GB vram, latest Forceware installed.
RAM: 8 GBs
Modlist / load order (BOSS'ed):
Skyrim.esm=1
Update.esm=1
Dawnguard.esm=1
HearthFires.esm=1
Dragonborn.esm=1
ApachiiHair.esm=1
JSwords.esm=1
Schlongs of Skyrim - Core.esm=1
SPIKE.esm=1
HighResTexturePack01.esp=1
HighResTexturePack02.esp=1
HighResTexturePack03.esp=1
Unofficial Skyrim Patch.esp=1
Unofficial Dawnguard Patch.esp=1
Unofficial Hearthfire Patch.esp=1
Unofficial Dragonborn Patch.esp=1
Unofficial High Resolution Patch.esp=1
BagofTrash.esp=1
cMKCustomStorageSpells.esp=1
SabreFurBag.esp=1
RaceMenu.esp=1
RaceMenuPlugin.esp=1
SkyUI.esp=1
Bandanas of Skyrim.esp=1
1nivWICCloaksCRAFT.esp=1
hothtrooper44_ArmorCompilation.esp=1
kimono's witcher silver swords.esp=1
skyforgedShields.esp=1
Dr_Bandolier.esp=1
Dr_BandolierDG.esp=1
Schlongs of Skyrim.esp=1
SOS - VectorPlexus Muscular Addon.esp=1
SOS - Dawnguard Armors.esp=1
SOS - Dragonborn Armors.esp=1
skyforgedWeapons.esp=1
ExtractOreSpell.esp=1
P1FlyingRing.esp=1
SSAPBWK.esp=1
vinis_transmute.esp=1
SimpleTeleport.esp=1
Teleport.esp=1
Teleport-DG Plugin.esp=1
Teleport-DB Plugin.esp=1
More Usefull Soul Siphon100.esp=1
Realistic Teeth Dawnguard Serana Vampire Fix.esp=1
Beards.esp=1
Brows.esp=1
TheEyesOfBeauty.esp=1
BHWarPaints.esp=1
ENB: Yes.
Any ideas would be appreciated.