One interesting aspect of the 140mm Macro lens, is how highly corrected it is for infinity work also. With my favourite 35mm lens, the Olympus OM Zuiko Macro 90mm f/2.0, it's really only so-so for infinity work, but I would have to say that at infinity also, the Sekor-C 140mm Macro is my sharpest Mamiya lens.
Here is a test I did (when visiting my parents at the coast) last year:
(Ilford FP4, taken around f/11, maybe f/16 - didn't make notes)
And a 100% crop, scanned on an Epson V700 scanner:
It's always amazing how much more grain shows up when scanning a negative than making an optical print, but it gives an idea of the detail resolved (scanner film flatness and focusing issues aside).