I have only unfortunate experiences with 20/2.8, Ais or AF.  I had used an Ais with my F100, but the peripheral areas are always soft, and the corners are always smeared.  Since then, I have tested around ten samples of Ais and AF on D750, but never found even a decent sample.  I have very good experiences with all of the previous 20s: f3.5 (52mm filter), f4.0 as well as f3.5 (72mm filter).
The quality of the images that have been posted by Longzoom look unbelievably amazing to me.