I found some more pictures in a russian discussion board.
Here is the translated thread (via Google Translate) with those pictures:
Sipix vs. Vizplex
Sipix vs. Vizplex (only the screens)
Sipix compared with a white background and perfect lighting conditions
Now the Sipix screen doesn't look that bad. It's background may be darker than the E-Ink's background but if you compare the blacks, especially on the second picture on top (the battery symbol on the Sipix and "NOOK Tour" on the E-Ink) then it looks better.
Comparison shots with Pearl would be great. And still no information if it has a plastic or a glass backplane. If the Sipix screens would be more durable and not so easy breakable as the E-Ink screens, I would be sold right away.
Greetz
Scheich Xodox