Sounds like a tech camera is your interest, but a few comments about the 645D. Iíve had my 645D since December 2010 ; like Milesí itís been in bad weather - snow, rain, blowing sand Ė not a hiccup. The files are quite malleable when used at ISO 1-200, above noise appears, but is easily removed. I have a large collection of Pentax 645 lenses and most are excellent with the 645D. The 120mm A macro, which clearly out resolves the 645D sensor, might cost $400 (and Iíve never heard of a bad copy); other lenses are of similar quality. I followed Lloyd Chamberís testing of the 645D very closely and supplied a few of the lenses he tested. He found some excellent and some wanting. I admire his intelligence and methodology, but he tested a random collection of used lenses (many 20+ -years-old). Understandably, he tested the lenses in a very rapid manner, his business model depends on getting subscribers and Pentax is not a big market share. Many of his tests were shots of the Stanford Memorial Church mosaic; a lovely mosaic, but the functional equivalent of the brick wall. One of the lenses I sent him he found to be so-so, but I find it to be wonderful for landscape - very sharp, no flare and little CA, but I have the luxury of time in my tests.
No tilt or shift (yet), but an adapter for a 4x5 view camera is available (you need to use LF 90mm+ lenses). You can also modify the excellent Pentax 67 55mm or 45 mm lenses with a shim in the lens mount for a fixed 5 degree tilt.
The D800 has driven Pentax lens prices are very low; they are an amazing bargain (not the new ones).