One thing I discovered after usage of my BeBook, is that you can convert PDF to RTF or HTML and have a suitable document for 6" displays. If the documents are mainly spec texts, then you should be fine with 6" device, otherwise with a document full of graphics and schematics then I would do as Harry said.
Check out my BeBook review site at
http://www.majgaj.com/bebook I wrote some usage experiences with PDF in there.