Well-known overclocker, der8auer, has achieved a CPU-Z validation run at 6.1 GHz on the i9-7980XE using LN2, but settled for a stable overclock of 5.7 GHz.
https://www.notebookcheck.net/Overclocker-pushes-i9-7980XE-to-6-1-GHz-with-the-CPU-alone-using-over-1000-watts-of-power.251656.0.html