Paul, I'm very interested in your findings as I shoot a lot of Neopan 400 and 1600.
I have found Neopan 1600 developed in Xtol at full strength to produce very nice tones and can be just as contrasty as Neopan 400. I have also found both films to produce fine grain with deep blacks, nice smooth midtones and retains their highlights well. I have printed from both 400 and 1600 up to 20x20 inch prints with creamy whites (on agfa paper) and silvery whites (on ilford paper) and each with fine grain. I am most impressed with these films.
If you need the speed (which I often do), 1600 at 1600 produces beautiful prints.
I hope you don't mind me adding my 2 cents worth.
Kind regards,
Nicole