I have a Fuji GA645zi and had a Pentax 645 at one time. The good about the Fuji is the size and ease of use. The zoom lens is as good as most primes. Shooting handheld, the lack of mirror probably makes more difference than the quality of the lens anyway. The bad thing about my Fuji is the loud focusing and film advance. I'm not sure how the other Fuji 645s are in that regard. The Pentax is amazingly quiet. I generally use my Fuji handheld for the kind of stuff you are talking about. Here is a shot at about 1/15s at 55mm. The relatively slow lens is really not much of a hindrance since it is easy to handhold at a pretty slow shutter speed. Here is an image with more average light. This was also at 55mm with an orange filter (I think). I was riding a bike and just had it slung over my shoulder with some film and filters in my pocket. Tough to do that with an SLR.