Thanks for the good work. Very interesting.
I had a quick look at the pictures here and from my K100D, and here's my conclusions on pairings that appeared similar:
K100D 1600 vs K-x 3200
I initially thought K100D ISO 1600 and K-x ISO 3200 have comparable noise.
I actually I went back and fed the K-x 3200 DNG through dcraw (using ufraw) as I did for K100D's i was comparing to. There's a fair degree of noise reduction in the K-x JPG here for this advantage. But comparing 1600 to 1600 they seem very similar, K-x's a bit better. The K-x 3200 does seem better than K100D's though.
K100D 1600 vs K7 1600
comparing K100D ISO 1600 and K7 ISO 1600 JPG have similar noise, but the K7 has 'cleaner' data. It seems like there is less chroma noise. Unfortunately thats a Raw vs JPG comparison.
On opening the DNGs with dcraw. Not as big a difference as I had expected. Hard to say which is better.
K-x 3200 vs K7 1600
K-x ISO 3200 and K7 ISO 1600 seem to have similar level of noise.
But again throughout it's range the K7 seems to hold more detail. By that I mean the noise is less artifactual/chroma based, seems to have less noise reduction applied. On opening the DNGs some of the difference in JPGs is due to K-x's heavier noise reduction.
overall the K-x does have a little less noise, but I don't think its a full stop better.
Keep me happy with my K100D for a bit longer.
I would like a bold yellow camera though.