When the Kx arrived, K7 owners who were more than content with their current bodies coveted the superior high-ISO (low light performance) capability of the Kx. At least I did. And while the K7 was a capable tool, I often found myself compensating for its weaknesses (which were limited to high ISO and autofocus continuous (AF.C) performance). Not so with the K5.
I won't go into the specifications since those can be found elsewhere but I'll give my overall impression - what I like and what could be better: + Great ergonomics. Love the compact, solid body which is identical to the K7 save for a heightened knob and elongated AF lever. I was even able to use the same split prism focus screen I had purchased for the K7. + Fantastic high-ISO performance - clean and offering far more flexibility than the K7. I'd try never to breach ISO 800 on the K7 whereas the K5 is routinely pushed past ISO 3200. While I wouldn't give it equal footing to a full frame camera, it's arguably the best APS-C out there in this application. + Outstanding dynamic range -- shoot in RAW and leave your graduated ND filters at home. -+ Improved auto-focus, especially AF-C compared to the K7, but not quite on par with either the D300s or 7D in AF-C. + User-friendly, easy to navigate menu system - white balance adjustments are a breeze. + Good WB and JPEGs "out of the box" -+ Yes, 1080p video but at 25FPS vs. 24 -- surely a firmware update in the future - Audio records at 32KHz sample rate - Only has a single SD/SDHC slot - would prefer dual with Compact Flash - Limited to 1/180 X-Sync speed - but this is ample in most scenarios - Images shot in portrait don't autorotate on playback - but did on the K7(?) - again, a likely firmware update + Blissful near-silent shutter + Compatibility with all those great manual K-mount lenses of yore.
Although I'm a long time Pentax user, I considered and evaluated both the Canon 7D and Nikon D300s without bias. While both are outstanding DSLRs, I preferred the Pentax K5.
An all-around excellent camera and a joy to use. A noteworthy upgrade.