My thoughts, try the lens out. I have realized that there is considerable sample variation on the 28mm. I am shooting with a 60MP back, you have an 80MP, so things might be different on the 80MP.
Thanks to Steve Hendrix, at Capture Integration, I learned a bit about the 28mm. I was looking to purchase a used 28mm, as I am slowly moving away from the tech camera environment.
Steve had 3 lenses, the Mamiya 28mm, the Phase 28D, and the Schneider 28LS. He was kind enough to test all three and send me the results.
Net, the Schneider 28mm LS, by far was the best. Less CA than either of the other 2 and more consistent in focus. The other two lenses, each had a variation in focus by a bit and the 28mm LS was much more even, and had less distortion in the lower corners. All three of these lenses had sharpness fall off in the lower corners, but the Schneider 28, had quite a bit less smearing. Are you going to get a single seamless shot with sharp focus from 10 feet to infinity, probably not, but Helicon focus allows for that.
I have used the 28mm several times now and no it's not as sharp as across the frame as my former 28mm Rodenstock, but with Piccure+ you can get quite a bit back. Impressive but very slow software BTW. (thanks to Graham for the tip).
So, if you are working with a dealer, and can try out the lens, that to me is the best solution.
It will be interesting to see if the Schneider 28LS gets a re-work sometime in the future.
Paul