Above left is my Daughter taken with the GFX and Pentax 67 105mm and on the right the same location a few months apart with the Pentax67 Film Camera using the 105mm lens.
A lot of Medium Format shooters are big fans of the Contax 80mm f/2 and for good reason. I was a huge fan of this lens on my Phase One. The problem with using this lens on the Fuji is:
A. The focal reducer for this lens actually reduces the focal length too much and you end up getting a very distracting Bokeh/Swirl effect on the edges and you end up with an image that looks like you’ve captured it inside a bubble.
B. The lens will cost you upwards of $1500 or more.
C. You can use and AF Adapter which is a positive however again your not getting the true focal length and not using the entirety of the lens.
D. The 80mm f/2 uses a very delicate focusing motor and from my understanding can be knocked loose easily causing focusing problems.
With the Pentax67 105mm 2.4 you can find great examples from $400 upwards. I would stick with either the Super Takumar Multi-coated version or the newest Pentax SMC version. These example will undoubtedly give you a better lens coating to handle flare and contrast. Focus is extremely smooth and you can still find the square style lens hoods but they can be costly.
For me the 105mm is perfect for my wedding work. I’m able to tell a story with this lens because it allows for so much of the surroundings to play a part. It renders an image that can be similar to a Large Format look whereas it’s just wide enough but the shallow DOF really allows your subject to pop and have considerable isolation. Single person portraiture is a must with this lens. The ability to capture razor sharp eyes and the rest of the subject features melt away are incredible. Again, a real large format look that is very difficult to achieve with full frame 35mm cameras and even some medium format lenses. The Pentax67 105mm makes easy work of this task. I’ve also noticed that the 105mm has a minimum focus distance of about 2 1/2 feet.