A55 is two stops worse than K5, fractionally better than the Kr. According to dxomark anyway.
Stands to reason that if you give the sensor all of the available light (instead of 30% less) you'll get better performance. It still might not be as good, due to the rest of the camera, but they key point is not a claim that it is a K5/D7000 rival, but that it is is Kr/550D/D5000 rival that might just top them nicely, slotting in somewhere between the two classes of camera.

After posting this morning I went walking around town for a few hours. Took a few pics (practicing rule of thirds composition, I'll post a couple later after I process them), and stopped in at the SonyStyle shop here. I had a play with the A580, A55 and Nex 5. They have a massive fish tank (maybe 3m x 1m) with several of each model of camera (different lenses on each) around it that you can take pics of. I'm kicking myself for not putting a memory card in and keeping some shots to post. Anyway.

It is an impressive piece of gear. I couldn't work out how to get more information displayed in the optical viewfinder, and I really don't like the shape/feel of the alphas so I'm not going to buy one. I tried taking the same shot with A55 and A580, in aperture mode. The metering was consistently choosing a faster shutter speed with the A580, but it was a very rough test - no tripod and I couldn't get the cameras in quite the same position (I was sitting them on the display bench).

Anyway, we'll see once there are some full reviews out I guess.

Btw: US$800 on Amazon now, with 18-55 kit lens. In case you're interested, hehe.