I have been trying to get across for some time just how slight a shade of neutral gray I have been advocating. And how big the results can be. I would put my projector in maybe the top 10% when it comes to brightness and the shade of neutral gray I selected is way down the sliding scale of grays that are talked about here.
Do the comparison as Tiddler mentioned I prefer comparing samples one at a time against a white screen. I used BOC as a base and advocated that in my thread because its something cheep and also something everyone can get their hands on a yard of. That way when we talk or view screen shots we are all on close to the same page.
I actually did my comparison at first with just the small paint cards you get for free at the paint store. I wasn't looking for overall PQ just areas on a frozen image where white and black came together. The slightest of gray deepened the blacks just as Tiddler said and whites seemed to change very little. There was a point when I could see a slight diminishment in white and that's where I stopped.
The resulting image was LOTS better than white alone and then the addition of the poly paint blend gave a slight improvement in brightness but gave an overall PQ increase in appearance. The word I want to use is not right there and it's something you have to see to know if its what you like. Glow, Shimmer, Transparent, Pop. Pick one
I ended up tailoring my screen to my new projector set on eco mode and brightness at zero with no boosts color 7500k all other settings at zero. I did this knowing throughout the life of the bulb I would need to bump it up from time to time by some means. That's how I would suggest others approach this also.
Side note: conventional wisdom tells us that lampblack mixes are known to result in a blue push. When calibration showed and I concurred by my own taste that 7500k was right for me based off of skin tones etc. I was once again a little surprised. I would have thought I would have had to go to a warmer 6500k at least.
Still haven't figured that one out.