I use an iso 40 film pretty regularly, and meter it at about iso 25. There are several at the 16-40 range.

For b&w work, I usually use a couple of 25 - 100 films.

For color work, I use a few in the 60-160 range.

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The nice thing is, that to make an 8x10 or 11x14 print, you are only magnifying the negative 2x or 3x, so grain is not much of an issue. 400 speed film appears to be less grainy than 100 speed film in medium format, or 25 speed film in 35mm, so your selection of film stocks goes way up - depending on the purpose, and requirements of the shot.