Photosku posted that size comparison between the three mounts. There are also overlays of the cameras (scroll below).
Nikon Z preorder links:
Nikon Z7 at BHphoto, BestBuy, Amazon, Adorama, Calumet Germany. WexUk. Jessops. CameraPro.
Nikon Z6 at BHphoto, BestBuy, Amazon, Adorama, Calumet Germany. WexUk. Jessops. CameraPro.
Nikon 24-70mm at BHphoto, BestBuy, Amazon, Adorama, Calumet Germany. WexUk. Jessops. CameraPro.
Nikon 35mm at BHphoto, BestBuy, Amazon, Adorama, Calumet Germany. WexUk. Jessops. CameraPro.
Nikon 50mm at BHphoto, BestBuy, Amazon, Adorama, Calumet Germany. WexUk. Jessops. CameraPro.
Nikon FTZ adapter at BHphoto, BestBuy, Amazon, Adorama, Calumet Germany. WexUk. Jessops. CameraPro.
Fuji GFX (red) over the Nikon Z:
Sony A7rIII (red) over the Nikon Z: