The windows power options are set the high performance, I have my voltage set to 1.285 and a 650w PSU. Currently I'm only overclocking to 4.0ghz, 3x increase from the stock multiplier. I've tried upping the voltage and it wasn't making a difference.
Just found this thread, in case you still haven't found an answer here goes:
Had similar problems with an FX-8150 on a GigaByte GA-990FXA-UD5 motherboard. My voltage, FSB clock and CPU clock were all fluctuating a lot under load. More details and my solution can be found here: http://forum.ocbase.com/index.php?topic=69.0
By design AM3+ motherboards use voltage droop (lowering CPU core voltage under load) and throttling (reducing Bus/CPU clock speed under load) to protect the CPU from damaging itself. These functions are unrelated to power-saving features like Cool n' Quiet, C1E, etc.
Some motherboards let you set LLC higher than default (this reduces voltage droop) and disable APM (turns off throttling).
Check if the BIOS on your Asrock board allows you to adjust settings to increase Load Line Control (LLC) or disable APM. In my BIOS these settings were found on the Advanced BIOS Settings page.
Hope this helps.