To be honest almost all current 6" ereaders are pretty much hopeless at reading PDF's. ereaders are designed to read ebooks and not document format PDF's so even with reflow and zoom, the experience gets pretty bad pretty quick. I tried PDF's on all my ereaders past and present and know how quickly it can become frustrating.
Of the Kindle e-ink ereader range, big is better and that would be the Kindle DX. It will still have all the same issues as above, but the bigger screen allows for less zooming and reflow issues.
Personally, I would recommend a tablet to view FFE's PDF's. I purchased an iPad2 late last year and it is superb in that role, will all the FFE rulebooks installed onto the tablet. Added bonus is, with wifi, I can use the interactive Traveller map online.