In my pinhole forays, I found that fast films called for too short an exposure in bright outdoor scenes to time reliably with a human-powered shutter (a true digital shutter -- operated by thumb and forefinger ). So I have gone toward the slower films to get exposures out towards 4 or 5 seconds with my gear. There has also been some suggestions that high reciprocity failure in some of the fast films actually results in longer exposures than some of the better behaved slower films like ACROS 100.