I checked out the other thread and put in a feature request (though I would argue this is closer to a bug report).
What do we currently know about the signal pipeline through Premiere Pro as it currently stands? Load/play a 1920x1080 clip into a 1920x1080 monitor and your observation is exactly what I'm seeing - on playback it behaves as though it is being scaled instead of passed through. Is this a monitoring issue only? Say the sequence is rendered out to a 1920x1080 file and contains 1920x1080 clips. Does it go through pixel to pixel or is there internal scaling and rescaling involved? Either one is a serious limitation but obviously the latter is the more serious of the two.
Currently, PP doesn't do monitoring properly. You need to either clone or extend the Desktop for it to work, which means Windows gets involved in the signal chain. That needs to go away. PP and other Adobe apps need to access the video port directly, so that Windows has no part in the signal processing.
Now that I'm actively poking at this problem I found a partial workaround, but it's pretty darned ugly.
Let's start with this: if I load a raw video clip into Windows Media Player and take it to full-screen on the secondary display, Premiere can no longer output to that display because it has been captured by WMP. So when I toggle to Premiere, the WMP image remains displayed on the secondary display even though Premiere has been told to use it.
BUT: if I load such a clip into WMP, go to full-screen, pause it, and then "worry it" for awhile (click the skip ahead button, right-click in the video to open a menu and select some choices, etc., etc.), eventually there will be a visible glitch in the secondary display. After that glitch occurs, the WMP file remains paused, but WMP no longer has the display captured. I can then toggle to Premiere, which will output to that screen. At that point the 10IRE boost to the pedestal is gone and the image has the correct tonality. It still looks rescaled (very close inspection shows stairsteps that are not present in a direct full-screen playback of the file), but a client sitting at the client table wouldn't see that. What they WOULD see is the correct tonal rendition of the image as opposed to the washed-out elevated-pedestal look.
The problem is that there is no set way to make this happen. It appears that I'm exploiting a bug in WMP to work around another bug in Premiere. I seem to be able to make it work 100% of the time, but it can take anywhere from two to five minutes to get WMP to "burp" in the right way. And since this is just some experimentation that I've done over forty five minutes or so, I don't know if this behavior would hold for an entire edit session. Naturally the process of trying to trick the display hardware into doing what it should do in the first place is something I wouldn't want to do in front of a client.
If this helps anyone's thought process on what the underlying issues might be or what a better fix might be, I figured it was worth posting.