You can read Letter/A4 sized pdfs on a 6" eInk reader by viewing, say, half a page at a time with the reader held in landscape, or zoomed into columns in portrait, particularly if your reader software allows you to crop the page to get rid of the margins. It's reasonably comfortable on my Sony PRS 650.
However, there's no doubt that a 10" tablet is a much better bet, and since getting my Touchpad a year ago I've not used my Sony for PDFs.
I'd love a light, A4 eInk reader, but the market seems to be moving away from even considering them.
Last edited by Graham; 09-13-2012 at 05:47 AM.