The first commercial laser printers were 300dpi and the result was quite readable (the very first one that was invented -- by Gary Starkweather at Parc -- was 500pdi). I asked John Warnock why 300dpi worked better than I thought it would, and he said that it was the "real black" and excellent accuracy.
We have both at least that on "retina" type displays, so I'm guessing that there is still some refresh flicker that is causing some of the problems (if so, then that would revise long ago experiments that indicated most people would not be bothered by anything above 120p).
(But I think I feel that my eyes are doing extra saccades on laptop displays, and that the contrast ratios and res are not good enough with eInk.)
The experiments I did at Parc, cross connected with Tom Cornsweet's work at SRI, showed curves that swung both with contrast ratio, and "distance from real black".
Another thing that will help (for "Aldus" type personal books) will be the next round of flexible displays that will feel a little more conformal.
(Also, how could the Ipad and Eink tablet folks failed to have put the batteries on one side of a symmetric device so it could be held with the center of mass in the offhand?) This is really shockingly awful elementary human factors design. The next round of these will hopefully have a lower density/mass in any case.
I have an older MacAir that does not have a highly reflective screen. The black is pretty good.
My feeling is that my eyes are jumping a bit with it, and for this (or some other) reason, I also have a distinct "I'm not remembering as well" underlying feeling. (This could be an illusion, or it could be harking back to long ago when I was trying to learn how to remember more of what I was reading ...)