DPReview has just published an article saying, in essence, hold on, medium format isn't all it's claimed to be, and perhaps you should consider sticking with a smaller format. They point out things like depth of field and availability of much faster lenses in full frame vs. medium format, and comparative resolution and noise to conclude there isn't much advantage.
I come at the decision to the Fuji from the other direction. I was already shooting medium format after having worked with the Nikon D800e. I much preferred the work flow and camera operation of the Pentax. I detested live view focus stopped down, and never could forgive Nikon for their backwards threaded lenses and rear caps. You'll note that this has absolutely nothing to do with the quality of the image, which is excellent.
But, how well a camera works in hand is very important to a working photographer. The more you use the camera, the more workflow and intuitiveness become of primary importance vs. a 10% or even 20% difference in absolute noise or resolution.
I'm finding the Fuji remarkably comfortable to use. The magnified view by pressing the rear dial falls exactly to where I want it. I found out this morning that I can make self timer stay on after turning the camera off - well done giving me a choice. Also, I'd been using the rear dial or fingering the screen to magnify made images in playback to check focus - turns out that again, a press of the rear dial goes straight to full magnified view, and back - so again I have a choice - do I want to zoom in on an image or jump to max. for checking focus.
The quick menu has a button on the rear grip, and although there are complaints on the net about accidentally pressing it - that has not been a problem for me and I much prefer this access combined with the touch screen for changing settings.
This, combined with the electronic first curtain, and the tilting lcd when in vertical framing makes this the best camera I have used so far. That the images are of superb quality using my Pentax lenses makes the whole thing fly.