See these:-
http://forums.dpreview.com/forums/readflat.asp?forum=1036&thread=36640450
Do note that the 6400 image was NRed, but still you can think about if the IQ is good enough or not.
http://www.clubsnap.com/forums/showthread.php?t=779686&page=2
The above crops are for the central part of the test pics only, which actually received good exposure. If you want to inspect the noise at different ISO speeds at shadows, just view the downsized full picture and I am almost sure that you should be able to spot the difference.
Also, a ISO 100, 6400 and 12800 downsized pics posted by a new K-5 Chinese user:-
http://forum.xitek.com/showthread.php?threadid=796029
(Text in Simplified Chinese)
Next, some K-5 downsized samples compared with the K-x from ISO 800 to 12800, with 800 and 6400 crops:-
http://www.pentaxforums.com/forums/pentax-dslr-discussion/118454-k5-vs-kx.html
And then finally here is a flickr set from a Japanese user, there is no EXIF in photos and the photos are small in size:-
http://www.flickr.com/photos/ippaiattena/sets/72157625044796715/with/5083584747/
Btw, some of the above samples seem suffer from severe underexposure. :-(
Still not satisfied? Just wait to see some full size un-retouched samples produced all by the K-5 (and with full EXIF info of course) to come in the near future. By that time, I am sure that you can measurbate endlessly, forever and for whatever you want! ;-D
Read Also:-
K-5 Will be Marketed Earlier
Sony A33 Brief Hands-on Impressions (w/ ISO Comparison: 100-12800)
NEX-3 Vs K-x Full ISO Shootout (Controlled Test)
Sony NEX-5 VS Pentax K-x ISO/IQ Shootout (Dual Scenes)
Sony NEX-5 and NEX-3 Hands-on Impressions / Quick Review