Hello,
I got my 902-black yesterday. It is my first ebook reader so I cannot compare it to anything else.
I put short video
http://www.youtube.com/watch?v=PmZ5xHdeDiI, showing chm, djvu, pdf opening & reading.
Please excuse poor quality without stabilizer
php_manual_en.chm was unable to open. File should be ok (success to open in win 7), so no luck there.
perl-5.10.0.chm (6.57MB) was opened in 51 seconds. During the reading there were no big delays. I tried to show all font sizes.
libc-2.7.chm (1.8MB) was opened in 21sec. This file is not in video.
RPA V15 No3-4 1998.djvu (1.7MB) opened in 7sec.
PDFs were from
computer magazine. Sorry for not English resource

The first one is black&white pdf, which should be (according to authors) optimized for readers. It was 18MB file, opened in 7sec.
Second pdf was 30MB, coloured, opened in 26sec. Both pdfs have about 4 sec delay before reacting to next page button. (which is OK when reading)