"you may need a screen as large as 75 inches or more to tell the difference [of 8k] versus 4K."
One thing I rarely see mentioned is that the viewing distance has the biggest effect on required screen size and resolution. If you're sitting 10 feet away then you'll probably need a 75" television just to be able to see the difference between 4k and 1080p (I'm guessing with average eyesight) let alone getting 8k involved.
If you're looking to buy a new television, I would strongly suggest checking a few online resources covering the relationship between distance, size and resolution before doing so.