HDMI
Some monitors use different circuit for HDMI decoding and graphics card see this as "HDTV" wchich can lead to all different kind of problems like need for 16-235 levels (those will produce banding even if set properly).
I don't know if this is true, but I do know a lot of people would suspect this as the culprit and would be wrong in doing so. If you've got an AMD GPU, by default, it will send 0-255 over HDMI. For Nvidia, it "assumes" that if you send audio over HDMI, then you're on an HDTV. So, HDMI + audio = 16-235, while HDMI sans audio = 0-255. It's annoying as hell and I'm still trying to troubleshoot it.
Due to another bug, any custom resolution automatically sends 0-255, so I used to be able to just do a custom resolution for my native resolution. Now, however, NV doesn't allow you to do that. They basically removed the "fix" that people like me used.