Hello Brince:
One major issue with shooting 6x7 and cropping for the panoramic on the Mamiya 7/7II is that you "still get ten shots per 120 roll". Shooting 220 is a good option, but that's becoming hard to find. When you load 35mm for panoramic, you'll get 18 frames and less waste of film. Unfortunately, you have to use more of the 35mm film leader when loading into the M7/7II than in a 35mm camera.
As others have mentioned, the loading and unloading is slow.