I'm not sure where some people got the impression that anything beyond the K-7's ISO 800, would look bad or is not good nor usable .
K-7 at ISO 3200 without NR.
K-7 at ISO 3200 with NR.
I believe it comes down to how utilize exposure adjustments. a k-x result would look bad as well at ISO 1600 or ISO 3200 if it were not exposed properly or necessarily enough to mask ISO noise. I'm not debating the fact that the K-7 is noisier than the K20D at High ISO, much so against the k-x. the point is, you will get worse images with any of these cameras if the exposure isn't right.
oh, and the K-7's ISO 1600 and ISO 3200 are useful. anything beyond ISO 3200 is suspect.