Originally Posted by worth
What are you going to watch on an 8K display? 80-90% of all current film and television production is finished at 2K, the remainder at 4K. 35mm film is generally thought to have somewhere between 3-4K of real picture information, depending on film stock, lenses, lighting etc. There's barely a noticeable improvement in 4K. So there's over a century's worth of material that will see no improvement at 8K. The only films that might see some theoretical benefit are productions shot in 65mm or 15/70 IMAX. That's a few dozen features, in all.
The best reason for 8K right now is filming which translates to superior 4K with oversampling.
35mm maxing out at 3-4K is debatable, I've read it can be as high as 8K, depending on those factors you mentioned, light and speed plus a 8K film scanner but over 4K may just be diminished returns especially if the output is still only 4K or HD.
After further examination, according to Wikipedia on 8K the ratio of screen size to viewing distance is 2.6. 2.6 is the ratio to determine how far away you must be before you can no longer distinguish individual pixels. So if screen size is 52" you would need to be viewing at 20" away. 92"/2.6 36" away, that's pretty close and in my case: 140"/2.6 is 53" or about 4 and a half feet.
That's more than twice what I'm sitting at now, however the 2.6 ratio is merely where 8K becomes distinguishable not where it becomes noticeable above a lower resolution which can be further out. I still think it would be noticeably superior to 4K at 140" and distance of 11 feet.
Since I haven't upgraded to 4K yet I'm not worried about it. I don't even know when I'll upgrade to 4K so this is likely 10 years from now before this becomes a reality and by then there will be more content.