I broke down and purchased one of these lenses. I have done two separate set of test shots and compared it with the 50-110mm HC zoom and one prime-- the 80mm HC. My shots were of old brick walled gates at Stanford (lots of unique cracks and lines) and a wood fence in my yard. I used a tripod and for one i used mirror up, timed shutter exposure to avoid issues of vibration. For both I used my Gitzo 1548 and cube.
The 35-90mm is exceptionally sharp at the lower focal lengths. It really beats the 50-110mm zoom at 50mm with the exception of the corners. In my opinion, the corners are weak with the new zoom and I am using the H3DII-31. My comparisons so far have been at f4,4.8,5.6, and 8. I have not looked carefully at the f11 and 16 images yet.
At 80 and 90mm, the difference in sharpness is very marginal and I could not honestly say there was a noticeable difference except at the corners where the 50-110 was a bit better albeit the difference in the corners was much less noticeable than what I observed at 50mm. The 80mm HC prime is still a bit better than the 35-90mm zoom primarily at the corners.
In terms of distortion, there were not huge differences that I could appreciate and pretty much corrected with DAC.
I have emailed a few others who have made brief but positive comments and both so far have stated they primarily shoot people and have not paid attention to the corners.
The lens is much easier to balance when holding and the AF is much faster than the 50-110 zoom. There is no question here.
My conclusion is that the new zoom is quite good but not without some faults-- the corner sharpness being my main negative.
I would really be curious as to results of others and if anyone has taken more landscape type shots especially with the H3DII-39, 50 or 60. Mark