The "magic number" (in my experience, others will certainly have their own experience, and comfort level crossing streams of varying intensity) is somewhere in the 500-1000cfps (~6.5 feet) for the Pemi, East Branch, in Lincoln. Above this range, then you have the beginnings of sketchier stream crossings. The higher / smaller the stream naturally is, the further up you can go on the gauge and still be safe. I use the mark of about 700 to be able to get to Owl's Head without heroic measures or wet feet. Basically, below 6.5 feet and 750cfps, I have no real concerns -- assuming a stable weather pattern, no snow melt due to warming, etc.
Tim