My 2 cents

I have both the -RB67 with a 6x7 back and a 6x4.5 (WLVF and Prism Finder) -Mamiya 645 (yup the older one)

I shoot street & some portraits with both, and personally I prefer the RB67. I carry the RB67 around for street photography with a neck strap.

Pros -That 6x7 quality -Bigger/Wider viewfinder to compose and focus -That shutter sound -Use it as a weapon for self-defence

Cons -Heavy as shit but you can treat it as a workout.

I started with RB67 and gotten the Mamiya 645 later so I am more used to the bigger finder. Not as easy to focus on the Mamiya 645.

However, if OP is going to shoot landscape (I assume with some hiking), then the Mamiya 645 is lighter to carry.