NVIDIA reference cards are great for overclocking on and the performance gains that are to be found are quite impressive. Whilst I stress that you cannot unlock a GTX 780 straight to Titan performance levels due to hardware alterations, overclocking is another way of getting that bit extra out of the card.
With both cards running on the same GK110 core, its safe to say that we can get a ball park figure in mind as to where the core will overclock to, same with the memory. Using AfterBurner as my preferred overclocking tool, the first steps to overclocking involve increasing the power target as far as it will go as this will obviously give scope for a better and higher overclock in the long run.
The GTX 780 jumped straight to the 1GHz mark without a fuss and slowly increasing the core in 5MHz increments, the GK110 core eventually started to cause driver crashes at 1050MHz, dropping this then back to 1045MHz resulted in a stable platform to work on with a new boost clock speed of 1084MHz. The memory clock similarly saw some impressive gains, rising by over 200MHz from 1502MHz to 1735MHz.
As a result of the impressive overclocks, 3DMark11 saw a gain in score from 4574 to 5282 which calculates to a ~15.5% gain in pure performance. For those interested this is higher than Titan at stock, although the mighty card when overclocked does still keep itself in the lead as expected.