Pair Titan X with which display?

I have a Titan X and want to add a monitor to my set up.
I am looking at Acer's 4k gsync and Asus's ROG Swift.
I would still like to keep both my old 1080p displays as part of the system if possible too. Do you guys know if the Acer XB280HK will be able to play most games at ultra and at 60fps?

I think you mean would your GPU run games at 4k ultra 60fps, the answer is probably not, maybe if you had 2. I think the benchmarks are more in the 40fps range for a titan X, if you wanted 4k gaming now I believe the 295x2 would have been the way to go.

Look up some performance benchmarks for the Titan X at 4k, then you will see how it runs games at that resolution..
and the quality of the rest of your rig.

JayzTwoCents did a pretty good review, the main benchmark for this is Battle Field 4:

Some more benchmarks here:

And of course we had to through in a Linus Tech Tips video (4k benchmarks start around 5:38):