I'd like to repeat a couple of thoughts from an earlier post - sometimes in a long thread like this things get lost - to help keep this discussion centered. If you're not planning on using shifts on a tech camera you can skip this post. :deadhorse:
If you're not shifting it's clear to me that there is no issue - the 80 meg (or any other non-micro-lens) back produces terrific results.
This is a schizoid thread. It plays to the insecurities of both new back buyers and schneider lens aficionados. I think your points re quality with the IQ180 speak to more general compromises of movements, and actually deserve a thread of their own.
Anyway, many effects of shifting bother me. Some of it is a function of distortion, defocus and MTF degradation (also present in the periphery of LF film). Some of it is a result of color cast and the effects of correction (unique to digital). Really, if A+ over large fields is my goal, especially with movements, I still love 8 x 10 images.
Getting back to deciding whether to take delivery of the IQ180, I do not get really high image quality in the lateral portions of shifted images. If I want top quality, I would probably not shift more than 5-10% of image circle on any MF lens that I have (Rodenstock 40, 70, 90, 135). So, my own insecurity is fairly specific. Can the IQ180 give me a good cast correction with a 10% IC shift with my lenses?
The answer so far is a clear "maybe", primarily because no one else can tell me what I will regard as good enough. Sigh. Take delivery, test, and sell if I hate it. The 180 is a superb tool for many applications so the market for used ones will be good.