[ProDigit]

The Glo HD, Kindle paperwhite, and Voyage all have the same size screen, and 300dpi.
The H2O is the only one with almost exactly the same screen, save for just a few less rows and columns of pixels, and slightly larger.
From any distance of 10in or more, i doubt you can actually see the difference, unless you concentrate hard on it.

I understand that the 200DPI from the Kindle PPW 2, and the 300DPI from the newest one, are quite noticeable.

I also understand, especially at smaller font sizes, that the difference is even more noticeable.
Theoretically, 8pt on the older screens, should give you the same charactersize as 12pt on the newer devices.
Likewise, while 8pt is still readable on a 200dpi screen, though letters are jagged up a bit, 8pt on a 300DPI device is so small you'd need a magnifying glass to see it, unless they somewhat applied a zoom factor on those larger dpi screens to make them visually the same size as on the 200dpi screens (which I think is the case)