Would like to join the 67 club. Pentax 6x7 or Mamiya RZ67?

I would second what halfaman said: the 67 is perfectly usable handheld. It’s not stealth, not even a bit. But you don’t need a tripod. 1/30th can still give you sharp images handheld. Depends really on your posture and hand and lens.

If you compared side by side P67 enlargements handheld vs solid tripod, you'd probably see a significant difference in quality unless the shutter speed was high, and the focal length of the lens short.

Of course, a flimsy tripod or head won't help much, especially when big teles are involved. You need something solid. In an emergency, I've sometimes rested the camera on a hat or pillow (or hypothetically a bean bag) atop a car roof or fence post, rifle-style. That can make quite a difference too.

That’s for sure, Drew, but this is true to some extent for all slr with mirror slap

My brother once sold pro gear, esp Linhof and Rollei. He'd demonstrate how superbly dampened the mirror of the Rollei SL66 was by setting an upright dime atop the camera on a firm table, and then trip the shutter. The dime didn't even tip. If you tried that with a Pentax 67, the dime would land three blocks away, and the sound would get mistaken for a sonic boom (minor exaggeration - but you get the point). My brother owned a couple SL66 kits himself, but nonetheless always wanted to borrow my P67. It was a lot more ergonomic and convenient for him to use.

I've have had an RB67 and still have a Pentax pretty extensive kit, Koni-Omega 6X7 and Mamiya press. I recently picked up a Bronica GS-1 with 50mm, 110mm Macro, 150mm and 250mm. That camera is quickly becoming my favorite for a P&S 6X7 camera. I actually prefer the handling of the GS-1 over the Pentax. Lens wise they are really very good. Rendering is slightly different, but sharpnes is tied. If my decision was based on how the camera was to hold up mechanically I would probably have to go with the old "tried and true" RB67.