http://www.pentaxfans.net/thread-142928-1-1.html
(in Traditional Chinese, Google English Translation Here.)
It is told that the cold weather resistance of the K-3 is really good, which is yet better than that of the A7R which the user also owns, despite that the water resistance of both is good enough, as commented by that user.
So, a bulkier body could help for better cold resistance. And, an all-metal body could be inferior, also a compact body as well.