I use f8 with my 80/4 Schneider Componon S (f11 for postcards), and either f5.6 or f8 with my 50mm lenses (EL-Nikkor 50/4 and Schneider Componar 50/3.5) I only justification for this is viewing the grain though the focus thingy (Peak Microsight) where it looks best, and the regular bleatings of people who say "stop down 2 stops from wide open". My exposure times for a 10x8 generally are about 8-10secs which I'm comfortable with in regard to burning and dodging (hardly ever dodge).