Few random thoughts...
First, I think when testing cameras head to head you can get distracted by minutia that won't effect you post purchase. The very nature of placing them side by side will lead you to pixel peep and look for differences rather than evaluating each on it's own merits. If one camera has 0.1 stop more DR, or 5% less noise in the shadows at ISO200, you will see it when placed head to head, but it's unlikely to effect your use of either camera if chosen.
Don't get me wrong, I think the IQ160 will perform exceptionally in this regard (pixel peeping vs an H5D). But it's not the area I would suggest you focus on. Truth be told I'm sure you'd be happy with the quality of a best-case capture from either system.
So do your head to head, side by side, same condition testing; you'd be a fool not to do at least some since you'll have both.
But I also suggest you save time and mental power (testing can be mentally exhausting) to focus on evaluation of each camera on it's own merits and as a start-to-finish part of your workflow.
Obviously my list will be biased, so take it for what it's worth, and of course ask your Hasselblad dealer for some areas that he'd want you to consider and test...
- Accessory size, fit, finish
- Build quality (durability/fit/finish)
- Required packing size for all necessary components
- Boot up speed
- Stability of the back (any crashes/freezes?)
- Speed of initial/final renderings after capturing a shot
- Speed to check focus in several spots in a given image
- Speed of switching between two similar images to compare focus/detail (also, does it re-render or switch between two fully rendered views)
- Quality of LCD (view-ability in the situations you'd use it in)
- Histogram quality, convenience/speed of access
- Unique Features (e.g. live view, focus mask)
- Software user interface
- Software speed and stability
- Software feature set (automatic horizon correction based on the back's virtual horizon, local adjustments, color editor, perspective correction, etc)
Regarding lens cast with wide symmetrical Schneiders:
- Make sure to check the box in Capture One 7 marked "wide angle lens" when using the 28XL and 35XL
- Both lenses usefulness with an IQ160 (and I suspect the H5D-50 as well) are improved considerably by using the center filters. If you don't have the CF I'd strongly suggest trying to beg/borrow/steal.
- The IQ160 works considerably better with the 28XL and 35XL than the IQ180 (which uses an 80mp sensor not available in the Hassy line). So any writings/reviews/opinions you've seen regarding the IQ180+28/35 do not really apply to the IQ160.
- It is pixel size, pixel design, and amount of movement from the center of the lens that causes lens cast. So an H3D-39 and H5D-50 should not be expected to perform similarly in regards to lens cast simply because they share the same sensor size.
- Don't try to equalize the variables like sensor size. Instead try to answer the question: with each back+lens combination, using best practices, how much of a given scene can I capture, and how big can I make a high quality print of the result? The IQ160 has a larger sensor so if, for instance, you saw lens cast 1mm of movement sooner than with the H5D-50 you'd still be seeing further into the image circle. It's not about how many mm of movement, but of what final image you can produce with each.
So anyway, this should be a lot of fun for you. Please let us know all your reactions!