Like Q suggests, get some Ektachrome and try your CF40 with film.
I own a CF40 myself and I cannot related to the problems you describe.
Not owning a digiback I have only used it on film myself. If you want I can post some TIFFs from images taken with the CF40. There are some on the forum but they (for reasons of image & file size) do not do the lens justice.
Have you tried another lens, keeping the camera & digiback the same? If yes, what were the results? For sharpness problems the problem can lie in the camera itself. Things an improperly aligned ground glass, incorrectly aligned mirror position or a bent camera (yes, that is possible, I have had one that was diagnosed with a couple of hunderdths of mm of 'warp'. A competent repair person can fix all that for you. But that person then also needs the proper alignment / measurement fixtures.
Another test might therefore be to take the lens plus digiback onto another camera and test what that produces.
More on the CF40: mine has been serviced by a retired Hasselblad repair guy then the FLE ring 'locked up'. While he inspected it he found another lens element which was slightly loose. His suspicion was that this might have been the case since day 1. I never noticed it in image quality ;-) The CF40 is a complicated lens (the FL elements do not help there) to work on, so only allow a skilled person to work on it. The FLE group being sort-of 'loosely attached' to the lens also makes it a bit sensitive to abuse, e.g. forces acting on the front of the lens. So always handle it with care, never store it on its front lens group etc.
As for the latest CFi40: I've been told by a number of people that the design limits of the CF40 can be shown using the top of the line digibacks currently available and shooting a suitable subject. I have not had the opportunity to verify this myself.
Wilko
NB: short of all this: send me the digiback and I will test if for you. Heck, I might even return it. At some time