Different animals. It isn't just the speed and grain that's different, but the latitude and saturation. Porta 400 is more a replacement for the
previous Portra 160VC, but at faster speed. Portra 160 replace Portra 160NC - a softer film sometimes more appropriate for portraiture. You
need to experiment with both. And then there's Ektar too, which pushes the contrast and saturation even higher, but nowhere near a chrome