To overclock today, we used the latest version of ASUS GPU Tweak with the Titan Black and Palit's own overclocking software with their GTX780 Ti Jetstream OC.
Both cards exhibited a lot of headroom over the default speeds. Even though the Palit GTX 780 Ti Jetstream ships in an overclocked state we managed to push another 17% from the core, peaking at 1,148mhz. The memory could be overclocked from 1,750 mhz to 1,914 mhz.
Nvidia's GTX Titan Black ships at a modest 890 mhz, but we could push it to almost 1,100mhz, translating into a 22.5% overclock. The GDDR5 memory on this card didn't quite reach the same peaks as the GTX780 Ti model, but a final overclock to 1,872mhz is impressive.
The manually tweaked speeds help improve performance significantly for both solutions. As we were able to push the GTX Titan Black to almost the same speeds as the GTX 780 Ti Jetstream OC, the results are very closely matched.