<< Solved >> No 4k Resolution with 6700k, GTX 1080ti

[slim.jim]

Whoa, I've got 4k resolution.

So, I had to use ResXtreme to force the highest resolution it recognized (2560x1600).

Then, I was able to use Settings > Displays to enable Overscan for my display (which normally results in a black screen). After enabling Overscan, my black borders were gone (image went all the way to the edges of the display).

Finally, I ⌥-clicked Resolution: Scaled and there was a choice for 3840x2160, which actually works!

Thanks for your help @Feartech and @jaymonkey. Greatly appreciated. Cheers.

View attachment 470992

If you are only getting 4K @ 30Hz then checking the Show low resolution modes in your screenshot will allow you to adjust the refresh rate.