This mirror slap nonsense has got to come to an end. I don't know if the 6x7 or 67 is worse than the 67II, but the latter is easy to handhold. I do it all the time, and I'm not afraid of "slow" shutter speeds. If you use the old rule of thumb for 135 cameras, which is holding the shutter speed faster than the reciprocal of the focal length, you're safe.
These are recent shots with the 105/2.4 on the P67II, all at 1/125 second, handheld. Each is followed with a 100% crop from the 2400 DPI scan with Epson V700 with its stock film holder. That's ~30 smooth megapixels.
100% crop:
100% crop:
100% crop:
Now, if sharpness is lacking, its NOT because of camera shake. It's because the scanner isn't better, the film wasn't flatter, or focus wasn't dead on.
With shorter lenses you can go even slower. I can dig out some 75/4.5 shots that is tack sharp at 1/60 if you want to see. That particular lens is very handholdable because of the high inertia and relatively short focal length.
Edit: Handholdability was the very reason I chose the P67II. I wanted an SLR because of my interest in well defined compositions, and I wanted a metering prism so I wouldn't have to fiddle with a separate metering device. I also wanted a very fast normal lens (the 105/2.4 is unbeaten for the 6x7 format, I believe), and finally I really wanted 6x7 over 6x6 because I like the aesthetics of the aspect ratio.