I was still uncertain as I drove to the store to return the loaned 645D and decided that I needed more certainty.
The issues were the money ($10,000), the lack of live view (I do a lot of focus blending), that with only the eyepiece I compromised flexibility at a time when I could really use a tilting LCD and live view to further flexibility, and a careful analysis of my own images with the camera and those available on the net to compare. I made prints and found I couldn't see a difference until I got up over 20X30 inches.
Today, I went out with the 5D2, and as dusk fell and I couldn't see through the viewfinder and as exposures moved towards 30 seconds and still live view worked well, I realized another advantage of live view.
Below are the images from this afternoon. The first had my 70-200 almost touching a chain link fence and there was a bit of fiddling to remove the hazy image of the wire. This was part of the demolished grain terminal in Calgary I had photographed before as it was being demolished.