PDF support on the Kindle DX is
extremely weak - I think that one would be hard-pressed to come up with any "strengths"

. No hyperlinks, no table of contents support, no searching, no annotation, the "no" list goes on and on, I'm afraid.
If you want a large-screen device and PDFs are important to you, the iRex devices (iLiad and DR1000) are currently really the only practical choice when it comes to eInk.