GF's PC performance dimishishing every minute in game (BF4)

[Smooth-Op]

I've started playing Battlefield 4 with my GF recently.

She's using my previous PC :
e8400 @ 3,0GHz (the value Gigabyte mobo won't even boot at 3.1GHz) 8Go DDR3 (don't remember the speed but it's value ram) HD6870 Standard 500Go HDD Windows 8.1
It's definitly aging but BF4 plays really fine on it even with medium/high settings producing 40-60 frame per sec. (fps) which is more than enough for my GF.

However, the game start stuttering after a few minutes and after some time it's simply unplayable with the gamefps fluctuating all over the place with an average of about 15-20 fps.
I would simply upgrade her PC if it wasn't of the fact the the game runs REALLY well for a few minutes... And it runs many other games like Left 4 Dead 2 at max settings without any issues.

I tried putting all graphical options to the minimum, reformating and changing Windows (she had windows 7 before), disabling many BIOS options that downclocks the CPU, checking the GPU and CPU temps to make sure nothing is "throttling", dumping the page file, running the game in both 32 bits and 64 bits, setting a FPS limit, closing every other program in the background. NOTHING made a difference.

So please! If anyone have an idea on what could be causing this performance detorioration in BF4, I would be extremely grateful.

 

[Smooth-Op]

Sounds like an overheating issue. Checked temps yet? HWiNFO is great for that sort of thing.

Yep, that's one of the thing I listed. CPU maxed at 60 celcius and GPU maxed at ~75 celcius.

Unless the temps were faulty, I doubt such temp can cause hardware to throttle.

Is there a program that could trace a chart of my CPU and GPU speed to make sure of this?

 

[Baralis]

I have seen a few posts around the web recently where people are claiming that windows 8.1 is causing them stuttering and freezing across a wide array of programs and games. Of the posts that I have read the solution was resolved by installing WN7 or another version of windows. *shrug* Perhaps not all the bugs have been worked out of 8.1.

This may not be the issue but it may be something worth considering.

 

[Smooth-Op]

I have seen a few posts around the web recently where people are claiming that windows 8.1 is causing them stuttering and freezing across a wide array of programs and games. Of the posts that I have read the solution was resolved by installing WN7 or another version of windows. *shrug* Perhaps not all the bugs have been worked out of 8.1.

This may not be the issue but it may be something worth considering.

That's another thing I listed as what I've tested as well.

Initially she was having the stuttering issues with Windows 7. I reformated and made a clean install of Windows 8.1 on her PC. The performance did increase by a whole lot (BF4 plays a lot better on Windows 8 then on Windows 7) but after 15 minutes, the crazy stuttering re-appears and makes the game unplayable with constant lock-ups every seconds and fps averaging 15-20.