I think the problems with low-light auto focus have been resolved. Early on, I had a friend who went through three K-5s before getting one that would work as well as his old K-10 in low light. But I mean low light -- below EV4. There was, however, a firmware update that helped correct the problem. The vast majority of K-5 owners never had any problems, perhaps because they never shoot in light that low. There were other models of cameras that have had similar problems. I have a suspicion that the rather extraordinary sensors available today just got ahead of the autofocus capabilities and the latter had to be tightened up.
Very much enjoy the quiet shutter. I'm in the process of a documentary, so I'm certain I'm not the only one who will appreciate the quiet shutter.
Just for the hell of it, I took a photo at ISO 12800 last night, in rather dim mixed tungsten/fluorescent light. Here's the result (70mm limited at f/2.4).
https://themotec1.netfirms.com/Users/Hosted/cdn/images/pentaxforums/attach/jpg.gif
DxO rates this sensor at a rather amazing 14 stops of dynamic range at ISO 80. 13 at ISO 200.
Really glad I finally got one of these.
BAB