Welcome to MobileRead, Tanager!
I like your Avatar, by the way.
Your conclusion about A4/letter sized PDF files and e-ink Readers is mostly correct. The 6" ones simply aren't well suited to displaying so large a fixed page rendering.
(I don't think this is what you meant, but the Readius probably won't be any better on that score
)
However, there is one device that has an 8" display, and, by most accounts works quite well for reading PDF files like you're describing, if you don't mind reading them in Landscape mode.
I'd suggest that you look into the iRex iLiad (there's a lot of info in the forums for it here), and see if what it does would work for what you need.
The biggest drawback for it is the price, being almost double that of the 6" devices, but of less concern is the battery life, which is 10~15 hours -- plenty for most folks, but not enough for some.
Hope that helps.
