I have benefited much from the advice on these forums, especially those who have discussed their experience with the 645D and various lenses, so wanted to share the results of acquiring a like-new barely touched 645D last spring and taking it on a multi-month trek across the West of the US. I began shooting in South Dakota in June, and continued westward making images in several different states, ending with autumn in SW Utah.
Most of the lenses were picked up used on eBay and I settled on a system consisting of 35mm A, 45-85mm A, 80-160mm A, 120mm macro A, 200mm A, and the autofocus 300/5.6 and 400/5.6. Lightroom 5 was used for development.
The 645D has exceeded my expectations. The 4:3 aspect ratio suits my vision very well, and the quality of the files gives me a similar feeling of satisfaction compared to my film days shooting 645N, 67II, and 4x5 field cameras.
I'm thankful to all on this forum who have shared knowledge and experience that helped me decide to make this plunge!