Shooting wide open will give you enough light, but perhaps not enough depth of field and depending on the lens less image quality.
Personally, I like the slightly soft look and shallow depth of field of f5.6 on 4x5. See some of the examples that Frank Petronio has posted that were taken at f5.6.
The smallest Alien Bees unit is rated at f11 at ISO 100 with a medium softbox, so if you can get it close to your subject, ISO 400 may give you f22, but even a larger softbox and greater distance should give you f11.
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