Unstable FPS

Greetings!

i am having performance issues the last two weeks and i have tried everything i could think off without any luck. I don't even know if the problem is gpu related.

Here's how the issue started.

i decided to update - flash my bios and the power went off in the process. i managed to reflash it but my ethernet port was dead. Since the bios update -I've made sure that the bios settings were the same as prior the update-, the pc post - boot times went up to 25 seconds and performance in games disappointed.

No matter the graphical settings, the same games that i could pretty much fps cap at 60 gave me anywhere from 30 - 60 unstable fps. By unstable i mean that the while the game playable character(s) are moving the fps goes from 60 fps to 30 - 40 and back at 60 within seconds. Sometimes it hits 0 fps, causing the screen to freeze. Also the character models will just appear out of nowhere.

I thought it was my motherboard. So i went to the shop and they replaced it for me.

Even with the new mobo, i am having the exact same issues. (The ethernet port is working tho ;p)

Pc specs :

• PSU: CoolerMaster SilentPro 1200W
  Mobo: Gigabyte x79-UD3
  CPU: i7 3930k
  Cooling: Corsair H100
  x4 Kingstone HyperX Geneis RAM sticks (16GB)
  GPU: GTX 670
  1 Corsair Force 3 SSD
  3 SATA 2 HDs
  

Things that i have tried so far :

• Prime95 CPU test overnight - stable
  Memtest86 overnight - no errors
  Installing latest GPU Drivers
  Installing latest Mobo drivers
  Clean format
  Upgrading from windows 7 to 8
  Modifying Nvidia control panel settings
  Disabling turbo boost
  Swapping gpus. - I had one gtx 275 and i tried to play the games with it. Although the fps were lower than the original card, fps were unstable as well.
  

I also tried a new PSU

I really have no idea what to do anymore

Below i've included one picture with the gpu,cpu etc usage while gaming. Also one 3dMark11 benchmark in case it is helpful to diagnose the problem.

Last but not least i tried the following :


So i tried to play diablo 3 to check my performance. I've played that game last year and i remember that it was smooth at 60 fps with everything maxed out. The results were AWFUL! FPS could go anywhere from 30 to 60 fps whenever i moved the character, used skills, etc. Sometimes it would stay stable at 60 but not for long.

Here's a picture of msi afterburner while playing.

http://tinypic.com/view.php?pic=21afhp1&s=5

Should i go back to the store and ask them to replace my card ? It is still under warranty :)

Thanks for your time and understanding.
Also i apologize for my awful English skills!