The first big mistake we can make is to look at the numbers on a film box and think that they describe the pictures we want to make. Neopan 1600 and Delta 3200 are both 'push films', low contrast films meant for maximum speed,
and speed isn't necessarily all that we want. We want a 'portrait curve' which lightly compresses the shadows, renders midtones naturally, and opens up the highlights without making them too dense to print. The problem with using D3200 or Neopan1600 is they tend to expand the shadows and midtones while compressing the highlights. So, we print on a higher contrast paper to make the faces look nice,and burn in the shadows. And compared to D400 @1600, they are grainy with low acutance/
If you use Delta 400, expose it at 1600, and develop it in DD-X
(using minimal agitation technique, which effectively 'pushes' the shadows whilst 'pulling' the shadows)
you end up with a fine grained image that naturally places the tones of a wedding where they are easier to print
than had you shot them on a low contrast film with a severe shoulder. The tone curve of the Delta 400 will be only slightly more contrasty than normal,and can easily be accommodated by using a half grade softer paper.
A good starting point for DD-X and Delta 400 @ 1600 would be 16' @ 20˚, and agitate the film
for ten seconds at the beginning, then at the 5th, 10th, and 15th minute. The result will be a nice, clean image, that is easy to print. The biggest reason that this works is the long, linear scale of D400 (and TMY2) that is easy to manipulate.