I have both iPAD3 and Kindle Touch. I also have a myopic diopter of -7.0.
From my experience, the iPAD3 don't fit for reading, especially for those verbose academic textbooks and papers. Because I find the vaulted retina screen has strong reflection rate. Both under sunlight or indoor environment, the screen generates confusing reflection. I have never managed to read more than 10 minutes on iPAD3. The strength of iPAD3 is video playing and casual game. The map application is my favorite.
For the kindle Touch, I usually feel comfortably to read continuously for 1 hour. With brief interval rests, I could read for several hours. The only obvious weak point is the picture displaying is terrible. And the contrast is not sharp enough. In general, Kindle is very suit for reading those largely consists of text. I heard of that Nook series would release a reader with glowing back light. As an amazon fan, I am sure I will buy one if there is a glowing Kindle.
If I need to read academic materials which is not suit for Kindle for a relatively long time, I choose to read it on my ThinkPad, which has a non-reflection screen.
I hope my experience would serve as your reference.
