I'm posting update to my Overclocking experience.
I waas not able to keep mobo stable at 400, so I reverted BIOS settings to all default. (Load Optimal Defaults)

I'm running on all default values, but STILL having ramdom reboots. It's looking like some driver issue or HW problem.

I have Auzen X-FI Prelude 7.1 additional PCI soundcard. (Integrated disabled.)

PC, reboots while no activity. While playing MP3, or idle, once I connected USB device (on HW driver installation buble right low corner), and once when I just started Everest.

This is totally weird. I don't think it's HW issue because, reboots would be more regular, related to some activity (heat or load).

I also tryed installing ATI Catalyst drivers 8.7. No result.