In my experience, medium format takes the most noticable descent after f16 with most lenses (both medium format and view camera lenses, yes even digital lenses like Rodenstock, Schneider, etc). Aperture use of f22 or f32 may be usable, but certainly not optimal compared to f16 and larger. Once I get into a situation where I discover f22 is the ideal aperture for what I'm trying to accomplish from an exposure or depth of field perpspective, I start trying to think of ways I can change that equation so I'm back at f16.
However, the degree of loss will differ as the complexity and optimization of lens design means that some lenses may perform stronger at smaller apertures than others. Recently I took part in some testing with the Phase One digital lenses against another brand of medium format lenses and the Phase One lenses in this test were sharper at f11 and smaller, while wider open it was a much closer contest.
The result of all this is that you may want to test the lenses at the apertures which you feel you will most commonly use. Obviously some applications require random apertures based on the situation where other applications may be more consistent in terms of the most often used apertures.
Steve Hendrix
Phase One
