just out of curiosity, when you did the shot with the cap on the body at iso 6400, how long did you set the shutter for?
I did 30 seconds and a 10 seconds. Then I mowed the lawn at full zoom. Thirty seconds was pretty good. Noise was usable. 10 seconds shows nothing. It was pitch black. Of course you can remap pixels by self cleaning like the mark II, I guess.