See these one by one:-
Pentax K-r vs. K-x ISO comparison A
Pentax K-r vs. K-x ISO comparison B
Pentax K-r vs. K-x ISO comparison C
Pentax K-r Measurebation - a set on Flickr
via Information on Digital Cameras (Japanese) and the brief post of the original tester at the DPR.
And the remarks by the author is quoted:-
"All photos were taken in DNG RAW and process with no additional noise reduction with the Pentax RAW utility that came with the K-r. I've included 100% crop "ISO elevators" for the convenience of the pixel peepers.
My conclusion from these pictures is that the K-r is not noticeably improved over the K-x."
As to me, it looks that the K-x has even slightly better Image Quality with clearer images and more details in all the comparison sets A to C linked above! The K-x even wins in noise actually. Oh, well.. :-o Pentax sucked quality from the new entry level body?