When talking about these specs:
-PPI (pixel density)
-screen resolution (number of pixels in horizontal and vertical dimensions) [800x480 pixels]
-display diagonal (distance from bottom-right to top-left corner of the display) [4.3 inches]
one must first realize they are entirely interdependent. Given any two, you can calculate the third. So, if you've got a spec sheet with all three, you are really being given the same information more then once. As it turns out, one of those three values isn't just redundant, but also much less useful than the others... screen resolution.
Why? Because screen resolution simply can't be a metric of quality by itself, whereas the others can. For example, a screen resolution of 1920 x 1080 might be fine for a 17" Monitor, but it would be absolutely terrible for a 27" monitor. The point is, you also need to know the size of the screen to decide if the resolution is good or bad, while the other two metrics can stand on their own.
That is why it is often best to ignore screen resolution entirely. It might be nice to know, but the only two that really need consideration are display size and PPI. However, note that the human eye can no longer discern individual pixels at PPI values above 300 at normal smartphone viewing distances (that is why Apple calls any screen with a PPI value above 300 a retina display). So, provided two screens have display densities well above 300, any difference should only be of concern to theoreticians (a.k.a. spec whores) as nobody will be able to tell the difference during normal usage. Debating the very small differences in PPI between the Lumia 920 and the 8X is somewhat nonsensical for this reason.
I know it's the phone with better ppi [8X] but I really doubt that the final effect when you look at the screen will be better than the 920's screen with ClearBlack and 60fps.
I agree. Contrast, brightness, reflectivity, etc. are all much more important than PPI. PPI only needs to be of concern if it goes below 300.
PPI = pixels per inch, and pixel density does count for something.
PPI and pixel density are the same thing... yes, I like nitpicking stuff, sorry
Beyond that, I would also support everything you've said.
