If you only read text PDF you are better of with PRS-950. PDF reflow is really great at PRS-x50 models.
On the other hand for PDF with pictures, tables and the same a bigger screen is always better. I won't recommend Kindle DX or PB 902 as i'm not comfortable with both but PB 902/903 has by way better and more PDF features as Kindle DX.
Be aware that it seems like Amazon won't improve the Kindle DX firmware to port the PDF features from the K3.
