Although the newer UC98 announced at CES operates at 75 Hz (at least with FreeSync). Early UM95/UC97s wouldn't overclock beyond 60 at all without skipping frames. Not sure about now. Also, most people have reported hitting 75-80 on the Dell version which released later.
It seems like the refresh rate tolerances for this panel have been improving over time... maybe it has reached a point where majority of units pass for 100 Hz. That's my guess, anyway.