[Mount81]

Ok, so sorry if I've missundercept something regarding the actual complains, or if i would be somewhat inexact or mistaken in these technical phrases and specific options,  specially regarding NVidia-side possibilities, but I have to add:

That's because Windows is only compliant at 8bit when anything higher than 30Hz.

-> Are you sure that's some PC/Windows standard regulation and not just caused by the (buggy) NVidia drivers? See: https://www.extron.com/company/article.aspx?id=hdmi2faq

NCP will show 12bit but later in the processing this will dither down accordingly.

-> "Dither" to what, 10bit or 8bit? Cause 10 bit -may- just would be fine, but as it's stated as "dither" and as preferably it would be better to stick to stock 10bit anyways, i guess what you name "dithering" should evolve some post-processing resulting a not-so-much-native PQ. Am i right on this one? So the 10 bit -even- in this case would be much better than 8bit, but why not just set the native output to 10 bit as the wast majority of the 4K sources jet would make it self-evident as they are also mostly 10bit. 

I wouldn't get too hung up on bit depth.  You could be doing more harm than good by introducing banding and everything at 8bit would be fine with little to unnoticeable difference vs 10/12bit. ->

I guess you din't see much 10bit vs 8bit bitdepth PQ comparison samples. There can be a HUGE PQ effecting difference in how color banding is detailed and refined between 10 and 8bit, with much and undeniable advantage for the 10bit side (sometimes may also be dependent on the source video, but many recent true 10bit videos will show this difference undeniably even for the most sceptic or verdant typed eyes). -> This all effects of course if you have also a proper 10 bit display to the do these "final" task.