From the Wiki: 'Refresh frequency limits for HDR video[edit]
Color depth of 10 bpc (30 bit/px or 1.07 billion colors) is assumed for all formats in these tables. This color depth is a requirement for various common HDR standards, such as HDR10. It requires 25% more bandwidth than standard 8 bpc video.
HDR extensions were defined in version 1.4 of the DisplayPort standard. Some displays support these HDR extensions, but may only implement HBR2 transmission mode if the extra bandwidth of HBR3 is unnecessary (for example, on 4K 60 Hz HDR displays). Since there is no definition of what constitutes a "DisplayPort 1.4" device, some manufacturers may choose to label these as "DP 1.2" devices despite their support for DP 1.4 HDR extensions.[49] As a result, DisplayPort "version numbers" should not be used as an indicator of HDR support.' The 650/850UK's are 4k @ 60Hz only, so this would make sense.