kreislauf: i don't want to be heretic or something, but shouldn't you compare ISO 3200 +/-2 with ISO 800 +/-0 INSTEAD of ISO 3200 +/-0 ? ISO 800 +/-0would be the same exposure time as ISO 3200 +/-2 and thus be more practical...?
i tried to overexpose my photos with +1.7 in raw mode and found, that most of the time in aperture mode with auto ISO i could instead do +/-0 and don't expose that long with stepped up high ISO settings...
ETTR is a method to make photos with more details and less noise by increasing exposure time as much as possible without overexposing the lightest parts where you want to have details. Increasing exposure time is made with the (+/-) adjustment. The (0/0) point is the exposure measured by the camera.
Comparing photos taken with these two settings show the advantage of ETTR. ISO setting must be the same in both photos. I made this test with different ISO settings to show how effective ETTR is especially with higher ISO settings.