diop Hi, I have a NUC5i5RYK. I don't think the hdmi port on it is great, because by default originally intel and MS set it for limited range, so you have to set it in the drivers or windows registry to output full range. That said, on mine I use a displayport adapter, likewise on the work laptop as well.. displayport adapter. Both are connected to the same old monitor I have. The NUC is DP to VGA and the laptop is DP to DVI. I left the hdmi port on the monitor for use of the snes classic toy. I would recommend not using the hdmi port on the NUC unless there is a second monitor to connect it to which I don't have.
Regarding the VBIOS, it's a good question. I'm still on bios version 246 of my NUC, but later versions of the bios had a minor VBIOS update which I have never tested because I just never went beyond 246 because it was stable. That said, one of the nice things about the NUC there is a jumper that will let you reset it and go back to previous BIOS versions, with one caveat, which is the newest versions included updates to the Intel management engine, and other "security" stuff and they won't let you roll back to older versions. The release notes state which versions this occurs on, so anything between a range can be safely upgraded or downgraded.
Video driver version number does matter unfortunately. On Windows 7 which my NUC is on, I left it at 10.18.15.4279 because I noticed earlier or later versions didn't jibe as well and then stopped checking after a certain point. For W10 I would likely have to test with different versions.
Ditherig does work on my NUC, but not very obviously because the monitor is already doing FRC.