OK, here are a few test shots. Not a very appealing subject and rather poorly lit with consequent underexposure of the books, but I didn't have much time and was testing for sharpness only. I hope they will help. Shot with the P65+ and 55 mm LS lens mounted on a Gitzo with the Cube and an electronic cable release with MLU.
All shots were processed with C1 defaults only, except I used the automatic Lens Correction tool for the Schneider 55 LS lens. Also the corner shots were lightened a bit in PS.
The first one is the full frame at f2.8. Focus was on the "Image Clarity" book in the center. (good choice, don't you think?) The next is that book at 100%.
The next three are of the extreme left side at 2.8, 4 and 5.6.
The next three are the bottom right corner, again at 2.8, 4 and 5.6.
You will note that there is a fair amount of light fall-off in the f2.8 shot - easily corrected of course.
This final shot is the same bottom right corner at f2.8 BUT with C1's corner sharpness applied at +100%. It lacks smoothness on the screen, but in print it looks perfectly natural.
My verdict is that this lens is very sharp at full aperture except for the extreme corners which also have modest vignetting of about one stop or less. They clean up nicely by f5.6. I haven't posted any f8 shots (ran out of gallery space!) but they show a further small improvement in contrast.
A keeper for sure.
Bill