Feeling foolish here, but I have no idea how to tell which camera goes with which test image. For what it's worth, I think I like the images from camera #3 best, though #4 competes closely on different criteria.
Camera 3 is the X20, formerly known as "the camera that lags behind all others".
Camera 4 is the Canon G15, which seems to be a pretty close match, at least with this focal length for studio scenes at ISO 100 and if you don't mind the color moiré. By the way, camera 4 needed 1/60s to produce an ISO 100 image that is just as bright as the image from the X20 at 1/80s, so it looks like "Canon is inflating ISO".
However, Canon's ISO inflation is not even half as severe as in the LX7 (aka camera 1), which not only used 1/40s for the same scene but still needed a boost of about +0.4 EV to match the normalized brightness (no correction needed with the X20 RAW). So Panasonic appears to inflate ISO by a whopping 1.4 EV compared to the X20 (at least at ISO 100 with this scene and under this light). I am sure that seriouscompacts and other forums are filled with threads complaining about this, right?
The G15 is using the same 4:3 aspect ratio and 4000x3000 resolution as the X20. It's interesting that the Canon and Olympus are showing moiré despite their (reportedly both very weak) AA filters. Of course, a different scene could have produced a different result. There are situations where the X-Trans sensor will show moiré, too.
The Olympus (camera 2) overexposed the scene at 1/60s and had to be brought down about -1/2 EV to match the other samples. However, this is a problem of the test setup, as all shots were performed in manual exposure mode. Interestingly and unlike the 3 other cameras, the LX7 was
not shot manually according to the EXIF data.