Having an issue with a few of my games. Only noticed it with Street Fighter X Tekken and Dark Souls Prepare to Die. Randomly (often), the games will decide to perform terribly, usually at half of what their respective fps is supposed to be. Sometimes entering a new area or resting at a bonfire in Dark Souls for instance fixes the issue temporarily. Usually though the issues do not fix themselves and are only corrected when I alt+tab out of the game and then alt+tab back in.
GTX 670 ftw 2gb (latest 306.23 drivers)
12gb Ram (3x 4gb G.Skill Ripjaws DDR3 1600)
Windows 7 Ultimate 64
Using DSfix 1.5 for Dark Souls (not 60fps)
That is strange the CPU temp (from the sensor on the motherboard) got to 127C which would cause a crash or shutdown well before it got to that but the core temps didn't get close and they are fine. So I suspect the CPU could be overheating but cannot be sure as some of the temps must be wrong. I suggest you monitor the CPU useage in task manager when it slows, if it goes to 100% then I think it must be throttling due to heat.
It's possible mobo isn't calibrated or cpuid is misreading the values. If he runs a benchmark like prime or furmark I'm sure he'll see a rise in temps without the shutdown.
Get msi afterburner or similar and check the clocks on your GPU when this slow down happens. I think it might be going into power save because those games are really nothing in terms of load for 670. Double check that your power profile is set to maximum performance to avoid any other power saving "features"
Lastly, as simon stated, do check utilizations on CPU/GPU/HDD. and double check your background processes.
lastly, make sure you've got latest drivers for your GPU
Also, someone suggested I try to use a program called D3DOverrider and force triple buffering through that. As far as I can tell (need to test it more) it seems to be working, but why would I need an extra program like that just to make the games work proper? I've seen some with similar issues to me, but it's not so widespread that I feel comfortable with that workaround. Doesn't seem right, I don't know.