What will be your 4k monitor?
It is not clear to me if you can run at 60hz with hdmi, the rtx2080ti cards have hdmi 2.0
I use a 4k monitor and found that I had to use a dp connection to run 4k resolution at 60hz.
This particular pc uses a GTX750ti to do the job.
You might consider a similar second graphics card for the 4k monitor, leaving the 3 dp connectors for the 1440P monitors.