Originally posted by pcarfan High iso sucks!,
Cannot agree more than that. It's true that K-x is better at high ISO than K-7. And maybe the K20D is also better than K-7. But once you go past 1600 on any of these 3 cameras, IQ starts to be seriously compromised anyway.
I've used these three camera (K20D, K-x, K-7). My K20D had the stripped pattern at low temperatures, sent it to Pentax for repair, they returned me a photocopy of the manual with the operating temperatures highlighted. I understood that they wouldn't want to acknowledge this known problem (there is a thread about it on this forum). At high ISO the K20D is applying NR (starting from 1600) and had this blue tinge.
When I got the K-7 I was immediately struck by the high ISO noise being less controlled than my K20D. But I didn't get the stripped pattern (and BTW this time the Pentax excuse wouldn't work as the camera is specified to operate as low as -10°C) and NR was applied at much higher ISO.
The other things to consider when shooting in low-light is the speed and precision of autofocus. That's where my K-7 was superior to my K20D. It's also superior to my K-x because I can easily use the TAv mode on the K-7 to optimize the ISO to be as low as possible (and on the K-7 there are 3 options for auto ISO). SR seems to be better at low shutter speed on the K-7 than the K-x. So in the end, I often get better pictures with the K-7 than the K-x despite the K-x high ISO capabilities.
Now if the K-5 can blend the K-x high ISO performance with the K-7 handling and improve the autofocus, it could be the almost perfect APS-C camera.