Something else to consider in lens selection is the possible use of on-camera flash. Using a Mamiya C330 TLR as an example, many people here have stated that the 65mm lens isn't wide enough for them. They prefer the 55mm. Fair enough. But...
A 55mm lens in a 6x6 format is roughly equivalent on the diagonal to a 30.0mm lens in 135 format.
A 65mm lens in a 6x6 format is roughly equivalent on the diagonal to a 35.5mm lens in 135 format.
Where diagonal coverage is theoretically full coverage. But practically speaking, because flash coverages are not sharp-cut spotlight outputs, falloff is usually even a bit worse in real use.
Most electronic flash units are designed to cover only down to about a 35mm equivalent field-of-view in 135 format. This means that an average flash unit used in normal mode will begin to show more pronounced vignetting when paired with the 55mm in 6x6, but will far more evenly cover the 65mm in 6x6.
If one's flash comes with a wide-angle option (usually down to 28mm, or so) that will work, but of course at a reduced light output level and shorter maximum distances.
This is why I have both the 55mm and the 65mm for my Mamiya. When edge-to-edge coverage does not matter (say, outdoor fill when the main subject covers only the central portion of the frame) the 55mm works great. But when the edges do matter (say, when the flash is the primary light source), the 65mm is the widest I reach for.
Given the chart back in post #9, it seems as if the 65mm in 6x7 format might actually be on the dicey edge. And the same for the 50mm even if a 28mm wide-angle option is used. Of course bare bulb is always an option as well.
Ken