Baam,

are you running in AHCI or RAID mode on that 790GX board when ACC is unavailable? Which BIOS version?

In some cases clocking thru SBIOS is better for finding the max clocks - especially with multiplier locked CPUs where you have to adjust HT ref. clock (and Memory clock) by more than 10%. Clocking thru BIOS allows the system to retrain memory etc that is impossible when tuning on the fly with AOD. On the other hand with Black Edition parts you should see the same results from BIOS and with AOD (assuming you dont need to increase HT ref. clock too much)