I'm in the market for a medium format back and I have been testing the leaf Aptus 65S the last few days. I'm pretty happy with the results but it may be out of my price range. My dealer suggested an Aptus 54S demo for a very good price ($6500), but I just looked at the specs and found out that the base ISO is 25. That's pretty low...does anybody know or have experience with the 54S and how fast it gets noisy. At ISO 400 the 65S was practically unusable. Any help, thoughts or input would be greatly appreciated. I shoot mainly tabletop but my wife shoots mostly people. We would be sharing the back.