The ZS6 is essentially the ZS5 in the body of the ZS7. The advantages of the ZS6 over the ZS5 include a stereo mic for movie recordings, a Mini-HDMI output for direct playback on an HDTV or monitor, and a 3-inch 460K-pixel display. The ZS6's lens, image processor, and sensor are the same for the ZS5, and as such we expect the ZS6's shooting performance and photo quality to be the same as the ZS5's.
The ZS7 improves on the ZS6 by adding a built-in GPS for geotagging photos, a one-touch record button for movies, a better image processor, and additional shooting options. It also has the capability of recording HD movies in the smaller AVCHD Lite format; the ZS5 and ZS6 record in Motion JPEG only.