10 bit screen and fountain stripes

I've installed a 10 bit monitor today and I'm trying to understand a few things.

First the monitor doesn't have a driver file so it uses the windows default. In UHD resolution the Nvida control panel only shows the option of 8 bit output depth.

If I drop the resolution I can set it to 10 bit. If I then increase the resolution the Output color depth drop down is gray.

Perhaps that is a hint for others.

I've done some tests and I'm pretty sure I'm seeing 10 bit depth.

SO... I think I'll create a interactive fountain fill from white to say 10%. If it isn't 10 bit I should see banding. I can't see no matter how extreme I make this test.

Which bring me to the question...

Preview fountain steps only goes to 256. So surely if that is the case I should still see banding? Not that I want to see banding but I would like to understand what I am seeing. Obviously I can't be sure that a gray box in the Nvida setup mean 10 bit.

0-10% I see no banding

80-90% I see some banding

0-100% I see some banding

What am I seeing here?

Is it 256 fountain stripes between any 2 colors? In my case white-black, or white-10% etc?

I'm assuming I have this right. So my next question is if this limit was increased in more recent versions?

Another weird thing is that on the 8bit monitor the windows close button is solid red on mouse over.

On what I'm claiming is the 10 bit UHD monitor those controls in the top right, mouse over say the X turn red then return to the default gray while the mouse is still over it. The same controls in Outlook 2007 and Firefox work correctly. That seems a bit weird as I would have thought this was windows 10 driven code and would not vary between applications. The same goes for the options box. Not that I care as it all works fine, I'm just trying to get a handle on what is going on as I'm making a bug report to Nvidia as it seems to me that without a monitor driver file their driver doesn't correctly detect the monitor features. Is that a driver issue or something in Draw X6?