Version 4.1.0 of the MSI AfterBurner overclocking utility didn't let us adjust the voltage of the Titan X and we didn't have time to work out why. Nevertheless, we were able to boost the clock speed by 250MHz, resulting in a base clock of 1252MHz and a boost clock of 1326MHz, which isn't far off the 1.4GHz Nvidia said they reached. The memory didn't seem to have much overclocking headroom so we left it at 1753MHz (7.01Gbps).
Our overclock was able to extract 16% more performance out of the GTX Titan X, taking the average frame rate at 2560x1600 from 82fps to 95fps.
This time when testing with BioShock Infinite our overclock provided just 4% more performance which was disappointing.
Finally, when testing how well our overclock boosted performance in Crysis 3, we found a 10% improvement in frame rate which was enough to overtake the R9 295X2.