Unlike Intel's 'K' and 'X' series parts, the Core i7-3820 is not fully unlocked, featuring instead what the company calls "Limited Unlocked Core." In the case of the 3820, we hit 4.3GHz as it's possible to use a multiplier of up to 43x. However, we went further by increasing the frequency of the base clock. The Asus P9X79 Deluxe has a base clock selection setting that can be set to 125MHz, 166MHz or 250MHz.
Prior to the v0906 BIOS, we were unable to get this feature working, yet with the latest BIOS revision it works flawlessly. Using the 125MHz base clock we had to drop the multiplier down to its lowest setting of 37x which allowed for a frequency of 4625MHz, which is a respectable 28% overclock.
Using x264 HD Benchmark 4.0, we saw a 17% increase in performance for the Pass 1 test as the Core i7-3820 hit 184.5fps, setting it only a few frames behind the 3960X at 4.40GHz.
CINEBENCH R11.5 saw a 22% boost in OpenGL when comparing the overclocked 3820 to the stock configuration. The CPU score also increased by 21% to 8.98, by far the highest quad-core score on record.