With scanned PDFs, it is often a good idea to pre-process them for a 6" device.
PDFread is one program that does this.
Open Inkpot has just introduced a basic PDF reader. I don't use PDFs much, and I had a hard time working out how it works. However, its options look promising - see the attached scan of the screen showing its setup menu.
If you post a copyright free scanned PDF I can try it on my EZ Reader and show you what it looks like under Hanlin and Open Inkpot firmware. However, I am not sure I am using the Open Inkpot PDF reader optimally.
There probably are new devices in the pipeline from multiple vendors using the Epson controller and 16 grey shades. The Sony PRS-700 (8 gray shades) and the Kindle 2 are the 1st two devices using this controller. The reason I bring this up is that it is much faster for partial screen updates and will probably be partnered with faster processors. I'm not sure this will help for PDFs, but most of the software development is probably now going into these new devices.