SNR: K5, D7000 and A580 at the top
The tendency of the Use Case scores has a direct correlation with the SNR measurement. The metrics for the top three sensors (K5, D7000 and A580) are identical from ISO 100 to 3200. After 3200, the K5 takes a noticeable advantage, but mostly because of the smoothing it applies to the file.
If these three sensors show very similar metrics, those for the a55 and the EOS 60D show more noise. In the case of the a55, SNR loss seems to correspond to the 1/3-stop loss mentioned on some forums. The loss of light induced by the semi-transparent mirror is certainly the origin of the problem. The a55 and EOS 60D have a comparable noise output, both sensors almost 2 dB inferior to the top three sensors. The difference is important, as 2dB means 2/3 stop.