My system specs are as follows:

AMD Athlon 630 Quad Core
AMD Radeon 6870 1g
6 gigs DDR III RAM
Windows 7 64bit
Skyrim settings are a mix of high and medium.

From what I gather, I should be able to run Skyrim on high settings and get a smooth 40-60fps (40 outdoors, 60 indoors). This is the case with vanilla Skyrim. However, after installing about 80 mods, my gameplay has been affected significantly. Now I struggle to maintain a steady 30fps, and often times the game will freeze for moments at a time, only to play smoothly after a brief "loading?" period.

This is most pronounced during large battles with lots of NPCS. The odd thing is that many times after the game "loads?" (essentially a game freeze upon entering a battle) the remainder of the battle will be smooth. Sometimes not so much.

The research I've done (lurking in forums, and reading posts about similar problems) suggests that the problem may be my CPU being unable to handle a lot of script heavy mods. I've turned down the graphics to low, and the problem is still there.

Does this sound like a CPU or a GPU issue? Does anyone have a list of mods that would be very CPU dependent?

Here are a few of the mods that may be the issue:

More Monster Mod (I love this.. hope it isn't the problem)
Occupy Skyrim
Duel Combat (I hear this is very CPU intensive?)
Texture Packs
Climates of Tamriel

Any help is greatly appreciated.

I'd wager that the texture packs are behind most of the drop in frames per second. A lot of mods use high resolution textures, which is great for the aesthetics but not so much for performance. I usually download the version with the highest resolution textures and then resize (and compress) them with 3rd party tools (http://skyrim.nexusmods.com/mods/12801/ or http://skyrim.nexusmods.com/mods/13529/) into a format that still looks good enough but also performs well.

Which texture packs are you using?