I had the SEL16F28 when I first got my 5N. While sharp in the center, it sometimes smeared the corners very badly, even stopped down. Strangely it didn't seem to be aperture dependent. Even off a tripod it would smear corners sometimes.
I sold the 16 and picked up a CV15, which has given me stellar service. Sharper across the frame than the 16 & no smeared corners. Unfortunately I am one of those 5N owners that experiences color shift/vignetting with both the CV 15 and CV 21 (and probably with the 28 if I ever find one).
While it adds a couple of steps to the workflow (convert to DNG, CornerFix) it's a batch process and not so painful that I would shy away from these lenses.
Overall, for me, the CV 15 is a better choice.