Apologies Confused Stu, completely missed your post with your Crysis benchmarks. Thanks v much for those, they are good goals for me to aim for
My 1080TI is just a FE one, so standard clocks. but last night with a little overclock to 4.2GHz and sticking the memory at their proper timings of 1600Mhz, I did manage to get to 69fps at 4K on same settings, so 10fps short of yours.
I then of course tried for an even higher overclock (primarily on memory as I have an inkling that it's more that than the CPU) and promptly borked my system. Depsite my motherboard normally being reasonably good at resetting itself from silly OC targets, it now doesn't seem to want to boot. oppsie. It was late last night when I got to that though, so i'm fairly confident I can fix it when i'm back from work.
In the mean time, I did find this lovely video from Digital Foundry,
https://www.youtube.com/watch?v=tbGT-u4i3EY which suggests that the CPU is indeed not the issue, assuming you can overclock it can combine it with some good speed ram.
In other news, before bricking my system, I did re-run VRMark having now turned off the silly power saving settings, and got a much more respectable 180fps