Originally posted by treebeard Well, I have seen threads like this over and over again. Yawn
Yes, but the OP is asking the question to look for opinions on his specific needs.
The K-5 build quality is what is inspiring the OP, and the K-5 focusing issues have been largely addressed with the K-5 II.
However the D600 isn't a bad camera in any stretch of the imagination, and does sport the larger format, notwithstanding the lack of added resolution its sensor provides over the K-5 in real life photography.
It is a choice one must make at the camera store IMO. Hold both camera, shoot with both for a little while, and have a good feel of their UIs.
Then make the decision based on your photographic needs.