There is a review and comparisons of landscape shots in Nihon Camera, June issue, which also has a Pentax 645 ad on the back cover.
Jpeg images (!) have been used for a full page comparison against a D3x. It's interesting how Jpeg is creeping back into test methodologies, especially since Nihon Camera has a full-page back cover ad for the Pentax so it cannot be suspected of bias towards the Nikon.
Edmund