I did a short investigation on the manufacturers' web sites. Came up with some surprises. Here, from Ilford is a spectral sensitivity chart for their three ISO 400 B&W films. The surprise is that HP5 and XP2 cut off a good portion of the Red spectrum, almost like old orthochromatic films. The data sheets actually warn about this, saying more exposure may be needed at sunset, or when using deep red filters. Delta 400 seems to cover the entire reds well. The Kodak Portra and T-MAX films seem to perform similarly to HP5 and XP2.