I suspect that I might end up using flash for the uber uber dark times when there's absolutely no light and even 1600 iso film struggles For the most part, I'm trying to stay away from flash as I really like the look of natural light.

I'm beginning to understand that I can't really "change ISO" without changing film or push/pull processing. Since I'm not particular about either of those options, I'm thinking that a 2 camera setup would be ideal. or maybe a 3 camera setup - 2 x 35mm and 1 x medium format 645, each with a different lens and each with a different film. one color, one black and white or some strange concoction.

For those who use multiple cameras to overcome the ISO thing (without using flash), curious as to what's your setup like?