Rich, I agree with your first three replies, but only up to a point and it is certainly my fault for not making my post clearer on this issue.
Yes, a bigger screen will enable more detail to be seen if the starting size is "too" small, at a given resolution. But beyond a certain size the still bigger screens will result in less detail as the content becomes too stretched to remain sharp and clear, hence my reference to how a 640x480 video falls apart when expanded "too" much.
One of the many benefits of going to 4k and then 8k is that for even large home theatre projector screen sizes (that very few of us have) such as 160"+ there will be no decline in detail, as would happen if we tried to show 640x480 etc content on such big screens.
On the extreme other hand, there has been mention on this forum of there eventually being 16k content, for commercial movie theatres, presumably IMAX size etc.
One reason for that is because someone has worked out or believes that even 8k content will not be enough (in terms of resolution, detail, sharpness etc) for such large screens.
Of course it remains to be seen if 16k content is ever actually created and projected.
In relation to your second point, my experience is just the opposite. I have a JVC HD550 projector with an average quality anamorphic lens and a 120" anamorphic screen. I also own a 50" Panasonic mid level plasma and watching a blu-ray of Serenity (a movie I am very familiar with) there is more detail visible on the smaller plasma than the larger projector screen. Again, these issues are influenced by what content we are watching and the relative size of the screens being used, as well as viewing distances, contrast levels etc.
As to your last point, there are at least two issues that I would like to comment on to try and explain things better.
Yes, for 4k content, at the screen size you saw, there was little difference with 1080P content because we have to go very large for 1080P to start to deteriorate. That is why I chose 640x480 because just about every user of the net is familiar with what happens to that resolution video when we try and play it on screens that are "too" big, as all modern desktop computer monitors are, when played at full screen size.
Secondly, of course, as you say:
"So screen size/viewing distance is indeed quite critical to fully apprehending the new level of resolution of 4K ...." but we don't have to go to a large screen size and close viewing distance to "fully" apprehend 4k to make it (or 8k for that matter) worthwhile. All we have to do is to see that there is a worthwhile improvement, for us as an individual, over 1080P at the screen size we choose at the viewing distance we choose. Of course, this is going to be our choice and no general chart or table of figures based on someone else's experience can really help us here, especially when we have so many different tv technologies (LCD, LED, plasma, perhaps OLED) and projector types (LCD, LCOS, DLP, LED, perhaps laser) available which will affect our decision.
To put it very crudely, there is an important difference here between "fully" and "worthwhile"
I hope this clarifies my original post, at least a bit anyway. Edited by catonic - 2/19/13 at 3:11am