It would depend on the applications, the screen resolution and the expected FPS.
For example the 1080 Ti would be a waste at 1080p for many users, but not if you want huge FPS from it (appropriate CPU included). On the other hand, if you want 4K and reasonable FPS, you're going to want a 1080 Ti. Realistically, if there's likely to be a bottleneck between the two, it will be the CPU.
All in all, unless you have specific demands for a high end gfx card and a mid-range CPU, I would save a little cash and opt for the GTX 1080 or 1070 Ti.