I just did a DreamColor upgrade of an HP 8770w just like you but my GPU is a K5100M. I don't have these weird BIOS version quirks that you do, but I have really terrible banding issues and the system (Windows 10 22H2) only identifies it as 8-bit and the nvidia control panel jumps the 10-bit to 8-bit when trying to change.
The difference between your system and mine is that K5100M is not officially supported so I had to do an inf mod to get it to install. It seems like the LUTs that come with the nvidia drivers are not designed for the LGD02FC display giving rise to these banding issues and somewhere down the display software stack it fails to recognize the 10-bit support.
I don't know how to fix this either.
