Have been shooting mostly with my 645D with my new DA 25f/4 and it's been very foggy so far (apparently the evening I arrived there was a fantastic sunset - I arrived around 11pm so missed it)
Pentax-645D-with-DA-25 by
singingsnapper, on Flickr
Here are a couple with the D800. Although both cameras have similar resolution (and the dynamic range of the D800 is incredible) they are at the end of the day different formats. So I find some shots work best with the 4:3 ratio of the 645D and some work better with the 3:2 ratio of the D800. Yes you can crop them to suit, but that involves throwing away detail. You can get equivalent but equivalent isn't necessarily the same. They are both incredible cameras.
The D800 shots are handheld
Niikon D800 Nikkor 24 - 70 at f/8 66mm 1/30 ISO 400
Wateredge-Boatshed by
singingsnapper, on Flickr
Chiron-on-WIndermere by
singingsnapper, on Flickr