All this sounds VERY interesting but just as a sanity check, Pythagorean's theorem does NOT confirm that a 9.7 inch diagonal screen will show an 8.5x11 PDF at full size even if you assume the original had 1 inch margins all around and the reader could trim off these margins. Admittedly it is closer than a 6 inch screen.
Personally I might opt for the 5 inch screen with wi-fi and touch screen, just because it would fit in my pocket better (and of course the price is "barato" - you can determine the meaning from the context.)