Which version of the Extreme Tuning Utility are you using?
2209 seems the latest BIOS version. But version 2111 is the latest version that can be downgraded.
On my board (DZ68BC) there have been several overclock issues after BIOS 0035 (which added support for ivy bridge). You can check the 2209 BIOS release notes and this forum if upgrading will help you, but I would be careful.