Thanks - I always like to remind myself that NEW isn't always BETTER just as image quality perfection can be overrated. I also still have my Zeiss Zf 21/2.8 which would technically been better overall but since it and the other Zeiss lenses I have feel like they're made from depleted Uranium, I prefer to travel with and use the smaller, much lighter AIS lenses on the Df.
I do think that the 20/2.8 copy I have is a real gem too. Very impressive results on the Df. I'm sure that the same lens on a D810 would drive me to distraction with the required CA clean up and higher resolution rendering. I use Piccure+ which I really really like for lens correction and sharpening - I disable all sharpening in C1. If you want to give your computer a workout, try Piccure+ as it does a heck of a lot of processing (start it and go grab a cup of coffee) but fixes up everything with these types of lenses with the exception of geometric distortions - that you still need to handle in C1 or PS.
Download lens correction software