Have you looked into workstation cards rather than gaming cards? I don’t know if you’d do a whole lot better with price v. performance, but just a thought.
Workstation cards are slower and more than twice the money. If the software used FP64 then workstation cards would be considerably better, but none of the restoration suites use it, so the Titan X is currently the fastest thing available within the affordability bounds of mere humans, the 1080 will make things more affordable and bring a little extra performance (9TF vs 7TF) where 8GB of RAM is enough, and the 1070 will bring good performance at a relatively low cost, i.e. slightly slower than the Titan X but less than half its price. (6.5TF vs 7TF).
The ‘twice as fast’ that NVidia are quoting is only for VR performance where the new cards only render high detail in the centre and low detail towards the edges, not on normal compute tasks.