I just added a more detailed list of PDF capabilities to the
E-book Reader Matrix. I'm not sure any EInk device with a 6" screen will meet your needs, but the two best options are probably the Sony PRS-600 and the PocketBook 301 Plus. You may be able to find a PRS-600 on display in a store to try for yourself. The PocketBook would be mail order, but it has the most full featured PDF reader software (see
Pocketbook 360 test diary). The Reader Matrix also lists larger screen devices, which are intrinsically better for A4/letter PDFs but are either expensive or not yet available.
If your scans are images in PDFs, then "reflow" won't work but there are programs that take one page (image or not) and make it into several pages for better viewing on a small screen.