Hi,
it sounds like your CPU is throttling and this is either by design or overheating. You may need to update the bios or check your cooling and if you are indeed getting bsod's then see this thread here and post the results:
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Edit,
I just read your post in the blue screen section.
It may be that the cpu is doing what it's supposed to do. Today's systems are designed to drop speeds and power if it's not required. If you notice the cpu is dropping it's speed in the quieter moments of a game or whilst using the desktop then that's usually normal.
Your CPU-Z shot looks fine and i also notice the cpu throttles between a multiplier of 8 to 38 which is why your seeing the drop in speed.
You could test that the cpu is...