I know you've done a lot of analysing of RAW files from the IQ250 and have come to the conclusion that this sensor isn't great, or "sucks" as you put it, with tech wides. What kinds of test files have you seen that have led you to feel very confident of that conclusion? I'm curious, because at this price and with (potentially) live view, it's a great proposition IF it works well with the Rodenstock 32HR when employing movements. Have you seen samples with clear blue skies, etc?
It has been a few months since I dived deep into it, so I have to trust my memory a bit. The issue is crosstalk, which in mild doses lead to desaturation and reduced color separation and accuracy, and in heavy doses to demosaicing artifacts. As it has a gradual onset (not linear though! Varies vertically vs horizontally and also depending on shift due to microlens offset, sensor is designed to be in center) some people will accept more degradation than others, and it will also be subject dependent. A scene with muted colors is less affected than a scene with bright colors etc. Overcast sky will probably work fine as the color will be similar to the LCC shot. With color deviating strongly from the LCC the residual crosstalk error will be more noticable. A plain blue sky will probably not be too bad either as it's generally low in saturation.
In short, crosstalk lead to various effects which is not really predictable. One scene may come out fine, another may be plagued with issues. I don't think it's a good idea to put any high end system into large levels of crosstalk.
The 32 HR will work fine without shift, but you can't shift much at all if you want to be free of crosstalk artifacts. Even the 40 HR has issues, possibly even more as I think it's a less retrofocus lens than the 32HR. If you shift and stitch to compensate for the smaller sensor size you will definitely have color issues, it you care will be personal. The SK28 has pretty gross crosstalk when shifted on a regular IQ160 but still some use it.
Apart from Doug's public files I've got some anonymous contributions (I work with a crosstalk cancellation algorithm and have had some success so far, but still far from production use). I have from the 32HR and 40HR and SK60 but no longer if I remember correctly (got some more files recently which I have not had time to look at yet), so I don't know where the breakpoint is where you can use without restrictions. As longer lenses tend to be less retrofocus you may need to step up to like 70mm or so before you are without crosstalk issues for shifted positions.
It should be said that I'm more
conservative and concerned about color stability than most others, so I'm sure some will be happy despite color issues. It does seem like most MF tech cam shooters don't mind some color issues as long as it's good in the center of the lens. Sharpness and resolution is for many priority 1, 2 and 3 and color is 4, the reason is probably because it's harder to evaluate.
To be clear: this is only a tech cam issue, the V-system lenses will work very well with this back of course.