I use the 1DSMKIII with L series primes and on occasion zooms and I can tell you that that image quality from the 5D MKII is pretty much as good as it gets from canon. I like the rendering of pentax cameras the images have more
texture in them than my full frame canon cameras are capable of delivering. You can see the difference in the prints, which is where it really matters.
I'm considering selling them in favour of Nikon though, considering that the canon gear belongs to my family everyone has to agree with my decision...Though I will sell the lenses I bought: I'm keeping that EF 200mm f/1.8L and 400mm f/2.8L IS I use my canons primarily for sports the 200mm f/1.8L is fantastic with a teleconverter...so is the 400L. Though the nikon cameras with their superior tracking AF and high frame rates, and unsurpassed high ISO capabilities are soon going to be taking the place of the canon DSLRS.
The pentax 645D fills a niche for landscape photographers. APS-C is good for general purpose photojournalism. However, a 40MP reduced frame 645 camera will provide the image quality I desire, especially the ability to make very large prints. Fine-art Landscape photography has been the realm of 4X5 and 8X10 view cameras and at last a camera manufacturer has made a self contained High resolution weather sealed digital SLR capable of surpassing 4X5, even matching 8X10*
I have been aching for such a camera to be made, that is why My family has stuck with pentax through 50 years. And with my pentax 67 800mm f/6.7 ED IF lens I'm sure the pentax 645 will be a very useful tool for my wildlife work as well. As you can see I have been
gearing up in preparation for a move to medium format digital at long last.
*especially in such a small package. My ebony 8X10 weights 5.5 kg fully loaded, my Horseman weighs 2.4Kg fully loaded (I have yet to hear anyone ask for recommendation for a walk around lens for 8X10 format
). Medium format digital backs on 4X5 view cameras are rather bulky; sure Sinar,Horseman,Alpa and Gilde has made some solutions in that regard but they have their own set of limitations and draw backs - notably the restriction of camera movements and the lenses designed for these backs often have restrictions of their own(smaller image circles which further restrict the use of camera movements).