Well, I was proposing things like:

• 1280x800 @ 9" =167 PPI
• 1024x600 @ 7" =170 PPI
• 1280x800 @ 7" =215 PPI

I'd see things on those the same way as on a 770/N800/N810 (800x480/4.1": 227 PPI), U820 (1280x800/5.6": 270 PPI), or HP mini-note (1280x800/9": 167 PPI), as they're all comparable resolutions. There's some others out there, too, but I'm too lazy to find the specs on any more.

Basic technique for high-res mobile devices: if you need to make out individual pixels, move the device closer to your eyes. But most of the time, you don't need to, you just need to read text. This is what antialiased fonts are best for -- the case where pixels are hovering about the threshold of visibility. And sure enough, they work beautifully on an N8x0 -- I can't afford a U820 to test at 270; but they'd certainly be fine (for me )on any of the screens I'm suggesting.