O.C. FX-8150 processor randomly underclocks itself at 100% full load.

I recently built a new rig with an FX 8150 processor and GIGABYTE GA-990FXA-UD3 AM3+ motherboard, with 4 sticks of 2Gb Crucial Dual Channel DDR3 1333Mhz memory.

I noticed in the documentation that turbo support up to 4.2Ghz is supported by default, provided the processor clocks down to stay within the TDP requirements. I have a very nice Noctua CPU cooler and a good PSU, so TDP limitations shouldn't be an issue with me. Since all 8 CPU cores have been fully tested to 4.2Ghz, I simply went into BIOS and changed the multiplier to 21x, and disabled Turbo Core, since it is already running at max turbo by default. All voltage controls set to "Auto."

I've tried disabling/enabling C1E, C6, Cool 'n' Quiet, and toggled Load Leveling between "Normal" "Extreme" and "Auto" settings, as well as disabling thermal management under "PC Health" in Bios, but no matter what, whenever I boot into Windows 7, it always exhibits the same symptoms, randomly toggling between 3.3Ghz and 4.2Ghz whenever I have all 8 cores maxed out. All system changes were made in BIOS prior to booting into Windows, and the system clock has not been altered.

Once I did try stepping up the Vcore voltage up by .025 volts (the smallest increment available on my board) but when I ran the fractal software, my CPU temperature sky-rocketed within seconds of achieving max CPU load and continued to climb until it hit 70+ degrees when I terminated the software. Temps instantly dropped back down to 40 or so idle, so I know the CPU cooler is doing it's job. It shouldn't be necessary to step the voltage up at all since the system runs perfectly stable at 4.2Ghz on stock voltage settings, and I'm afraid if I try to undervolt it to meet the stupid TDP requirements, it will make the system unstable.

Windows 7 runs perfectly stable at 4.2Ghz, and I simply want to run my fractal rendering software (it uses 64-bit integer math calculations on all 8 cores) @ 4.2Ghz without the system underclocking itself. I don't mind the fact that the motherboard drops the CPU clock under idle conditions to reduce power consumption, but whenever the CPU is 100% utilized, I want all 8 cores to clock at whatever speed I tell it to and stay there.

I have checked the system clock with CPU-Z, and periodically, the system randomly underclocks to 3300Mhz (using a 16.5x multiplier instead of the 21x I set up under BIOS) while running 100% CPU load across all cores. It's annoying because this negates a lot of the benefit of overclocking my system in the first place. Speedfan is reporting an average CPU temperature of about 54-56 degrees Celsius while the fractal software is running, so I don't see why the system should have to periodically throttle down the CPU.

Like I said before, whenever the CPU is 100% utilized, I want all 8 cores to clock at whatever speed I tell it to and stay there.