[tbrownaw]

Really you need somewhat higher resolution.

Apparently 20/20 vision is defined as being able to distinguish things 1 arc-minute apart. This comes to 114 dpi at the 30 inches away that I just measured my screen at. And yet when I pick a small-but-generally-readable font, I can see that for example the leftmost leg of an 'm' looks different than the other two.

So I would say you want sufficiently high resolution that pixelization artifacts aren't visible, which means that adding or subtracting one pixel from a one-arc-minute item leaves it still at one-arc-minute. Maybe 2px/arc-minute would do this well enough, maybe it would take 3. But 1px/arc-minute still permits visible artifacts.