This one is already a good low light performer. Wonder how much better the K-5 II is.
I have both the k5 and the k5iis. The k5 did well in low light, but there were times like in a dim karaoke room where it was tough to focus (that's shooting iso 25600 at f2.4 at 1/30th... I mean it was theater dark) so I ended up shooting manual focus most of the night. Here are the pics from that night:
karaoke night [flickr.com]
At the very least, you can get an idea of what the camera does for noise in low light and insanely high iso...
Now the k5ii is more sure footed in low low low light... it focuses faster and hits the spot more frequently. But in a living room w/ decent light, the k5 does fine. There are some lenses that focus faster than others (when someone says a lens is a "fast lens" they are usually talking about the aperture, not how fast a lens focuses. It's called a "fast lens" because with a larger aperture, shutter speed can be increased to capture fast(er) action thus the word/description "fast"). I've used quite a few lenses, if you have some questions as to which lenses focus fast, let me know... and no, the kit lens is not one of them. Here's a set of photos taken in average indoor low light w/ the k5 in autofocus.
dinner w/ jo and tony [flickr.com]
By the way... the kit lens picture quality wise is pretty good when stopped down and when not used near the minimum focal distance. And if you want to get a WR lens that can handle a medium/heavy rain shower, the DA 18-55wr is about $150 new or $100 used which is pretty awesome for a WR kit (try pricing that out in any other brand...).