I don't know about 6.8μm, both of my backs are 9μm, but I would think that for the combinations of tilt and shift you are talking about it would be fine, especially at mid range focusing distances. I almost exclusively use it between f/11 and f/22, unless I am shooting wide open for shallow depth of field or stopped down to f/32 for macro work. The lenses really are that good.
People forget because they are old and now quite inexpensive on the second-hand market, that this was Fuji's premier camera system "back in the day" I remember pricing a kit new and it was over $30,000 with three lenses. This is top quality gear, have no doubt about that. Yes it is big and heavy, but for studio work it is perfect, and I do use it on a 9 foot Cambo UST camera stand, a tripod is not really the best option.
I have used it on location with both digital and film, and it is doable, not really any harder that shooting with a RZ67 as even though the Fuji is marginally bigger, they weigh about the same as the Fuji uses some composite and the RZ is all metal.
I can best put it this way, for some things it is the perfect camera, for others not so much, that is why I also have a Hasselbald H1 that I can put the Aptus on to shoot people in the studio, and an A99 when I need to work fast on location.
I have two GX680s and "you will have to pry them from my cold dead hands" I believe is the phrase I am looking for.
Kind regards,
Jason.