comfortable reading all depends on the person reading. with my 6" I need to use calibre to reformat pretty much every book I get because too many have a sizable margin and I need a 26 font. with a 26 font and no margins I can get 150 - 160 words to a page. with a large margin (which can get larger and larger when the font is increased) I would get 50 - 70 words per page which is really annoying.
I had been looking at the iRex DR800 because it's 8" and is still about the same physical size as a 6" reader but I decided against it and I guess that's good because they went bankrupt. I keep hoping I will find something else similar, but with calibre the 6" is still usable.