I don't know if this will be useful or not, but here are some scans of Portra 400UC prints:
http://www.bigdayphoto.com/5866093/ The people pics are from the underexposed roll - "ash" and "derek1" are definitely underexposed. I had an 8x8 made of Derek2, which is pretty close to properly exposed. Grain is about what you'd expect. Skin tones are ok so far. I think Portra 400UC is basically rebadged Max 400. :) tv
