I shall try and give a summarizing comment on the tech wide angle performance.
This sensor is not designed to handle the relatively steep angles coming from Rodenstock wides. The sensor is pushed into crosstalk (ie mixing of color channels) with the 40HR. If we do not use the full 90mm image circle but keep within 70mm the crosstalk means some rolloff in color separation ("tonality") and saturation, but you won't get a total breakdown. If you shift hugely say 25-30mm you will get total breakdown with both strong desaturation and residual color casts. The breakdown can come a bit sudden as the sensor is designed with offset microlenses along the sides (ie to perform best with the lens centered).
Considering the color fidelity and tonality aspect the Credo 50 + 40HR can be compared to using a P65+/IQ160/IQ260 with an SK35. You have similar type of limitations of image circle use, and similar type of tonality falloff due to crosstalk. If it's okay to you is your decision.
Looking at the real-world results of Guy's test here and Doug's IQ250 tests and also doing some measurements on the LCC shots I'd say that you will very likely get good results if you keep within that 70mm. There is a clear amount of crosstalk going on, but the effect is hard to detect in a real image, there is not much desaturation in practice, you could argue that within this 70mm image circle the increase in noise due to vignetting is worse than any tonality loss. I think the Digaron-W 32 will work too, and if we're lucky the Digaron-S 28 works as well, as the wider angles seems to be a bit more retrofocus than the 40. I would not bet on it until thoroughly tested though.
Personally I don't think the SK35 on the IQ260 is a good idea, and I don't think the HR40 on the Credo 50 is either, but that's because I'm allergic to paying for image circle I can't use and as the engineer I am I don't like pushing sensors into the operating space where they're not designed to be, and I guess I have not fully come to peace with that tech cam users in general cares more about sharpness than tonality . Still I'm less skeptic about the performance now than I was before. The reason is that I had seen some results of overshifted frames and then due to offset microlenses you get the effect that an area of the image circle that works okay with a smaller shift breaks down, so it looks worse than it is.
So if you can accept working within 70mm image circle and accept a little shaky tonality performance when shifting this can be the next big thing for tech users, live view at last!
Those that like to use tech wides and sensor design that actually match, 40/60 MP Dalsa and the Digaron series is great, and 50 MP Kodak and Schneider Digitar series is also great.