Game causes FPS stuttering which affects the whole PC.

[Mitsuma]

Hello,
I have this weird problem with Final Fantasy XIV ARR on my PC.

The game runs rock solid, 60+FPS in pretty much every area. (On Maximum, 1080p)
Only about 30-40FPS in a really crowded area.
The problem I have is a really weird FPS stuttering, that not only affects the game but
also affects my entire PC.

To show you what I mean I recorded a video with my phone because the stuttering would also affect my recording.
http://www.youtube.com/watch?v=rmInR_tz3bA
The video shows the game, a gif to the left which should be the example how it affects my PC and a timer running on a tablet to show that the video has not skipping/stuttering.
The first half shows how it affects my PC in areas where it shouldn't have any problems, the other half or near end shows you when I log off and on and extreme stuttering during loading screens.

The problem can get really annoying to the point where I can not play the game.
A good example is in Primals, Garuda and Titan Ex can get as worse as up to 3s of FPS stuttering, where my whole PC seem not to react.
There is no spot in the game where I really don't get this stuttering.
Only some places where I get less of it.

Now to technical details:
My system:
Windows 7 64bit
Intel Core i7 3930K (OC to 4.0GHz)
ASUS GTX 670 DirectCU II 4GB
32GB Patriot G2
ASRock X79 Extreme6
240GB Crucial M500 (OS, game is also on this drive)
2x 1TB (Games/Storage)
120GB Corsair Neutron (Games)
Corsair AX750 750W

I already made a topic in the German subforum back in September but nobody could help me there and some mod just moved it to the "resolved issues" forum.
Here are two screenshots from back in September that show the GPU usage during those FPS stuttering.


This one shows an extreme case where I wasn't even moving and the problem occurred. (Click for larger image.)

This image shows the same but during normal gameplay.
(It shows, top to bottom, Power%, GPU temperature, GPU usage and GPU fan speed)

Now the long list of things I already tried but didn't help or showed next to no effect:

• Trying different GPU drivers. (314.14, 314.22, 331.65, 331.82, 331.93, 332.21, 334.67, 334.89)
• Every version listed above was tried with a clean install.
• Trying several different combinations in the nVidia control panel.
• Trying several different in-game options.
• Fresh re installation of Windows 7.
• Clean install of pretty much every driver on my system.
• Trying FF on my main SSD, on my two HDDs and on another SSD.
• Trying some regedits for CPU core unparking.
• Looking around the internet to find possible solutions.

Thats pretty much all I can think about at the moment.
I really hope somebody could help me with this problem.

Small update, see post below.