Upon extensive research I am sorry to inform you that no one has done that very comparison and I do not own nor know an individual with that card.
It is still fairly new.
But
I did find out that the Titan Z supports newer versions of opengl and has dual precision rendering unlocked where as it is locked on the 780 ti.
The titan also has twice the size frame buffer thanks to the double vram.
So long story short the 780 ti is better at gaming but with all the other things accounted for the titan black is better prepared for 3d rendering it will most likely excel at it.
Hope this helps.