CAMERA WARS - GX680 is the boss, RB67 looks small next to it
Fuji GX680 to the left and Mamiya RB67 to the right
You get a lot of convenience with the added size of the Fuji, it's not just the 6x8 format (it's true there is a 6x8 motorized back to the Mamiya RB67 Pro SD, but that isn't an integrated motorized system as much as the Fuji is). You get built in motordrive, tilt/shifts/swings (like on a large format camera,), a very big and easy to focus focusing screen (although I have a Beattie Interscreen as well), and in my case auto exposure and flash metering (since i have the optional ae chimney finder). And lenses are as sharp as they come, no softness wide open here, no need to go to f8 or f11 to get sharp results. I'd call this tack sharp www.flickr.com/photos/androgynousectomorph/2457035932/siz...
However, the RB67 has a much more classic feel to it with everything being manual, it has a mechanical shutter (so you can always shoot with the camera, no dependency on batteries, only the optional metered prism finder that I have needs batteries). It's rock solid/metal/brass whereas the Fuji is 80's plasticorama.