Is it because the mainboard is not HDMI 2.0 or does not support DSC (Display Stream Compression?) (https://en.wikipedia.org/wiki/HDMI#Refresh_frequency_limits_...). Raven Ridge supports 2.0, but it's down to the mainboard to also support that.
Under the HDMI section indicates up to 5Gbps video bandwidth (in addition to 8 channel audio). So on the surface it sounds like I shouldn't even get 30fps, but I do. Thank you for the info, it looks like the board isn't up to the task via HDMI so I will make the effort to find a Displayport adapter. That PC has a LOT of life left in it and I'd like to get the most out of it ;-)