Using a DP-HDMI cable rated to carry UHD (3840X2160 @ 60Hz res), have tried 2x, Insignia 43" UHDs, 1x, TCL, 1x Samsung. None will run UHD @ 60Hz. They either switch to 30 Hz when "save change" or won't run UHD at all (the TCL).
However my LG TV does run as monitor @ 60Hz from the same set up...