Originally posted by GeneV It seems to me that the OP has defined away most of the K5 advantages as being of little interest. When finances permit, I will be getting a K5 because I do use the higher ISO of my K-x frequently, do need AF assist, and would like a more professional feature set for my high ISO machine.
However, as a long time K10d owner, I would have to say that its quality at low ISO, especially with controlled lighting, is unsurpassed by any of the higher resolution sensors I have used such as that of the K20d or K-x. I can't say I miss the pixels much between the K20d (getting close to the K5 in megapixels) and the K10d if I can expose for a true ISO 100. That is, however, a great big "if."
It's important to note that even at base ISO - in fact, at EVERY ISO - the K-5 has significantly higher signal-to-noise ratio. It supersedes many previous generation FF sensors and comes close to current crop in many ways.
With my K20D, I didn't often touch that "fill light" slider in LR3. The K-5 makes it a regular friend. It's like one-shot HDR of the sort that doesn't 'look' HDR. Plus, the noise in the shadows, even when pushed massively, is much less obtrusive and much more attractive than the K20D/K10D produce. I've gone back a couple of times and played with landscapes I shot with the K20D, and there's no comparison.
But, like I said, if landscapes are your gig, you cannot beat stitching, and a good stitching program like Autopano for a couple hundred dollars might serve you better. This is a 40 mpixel image (well, it's a down-sampled jpeg from one). In the original image, you can count tree-tops. This could be printed at 300dpi more than 60 inches across: