Both the 6x7 and 6x4.5 negatives are very close to the
4x5 ratio. A 6x7 measuring 56mm x 70mm has an exact
4x5 ratio. A 6x4.5 measuring 44mm x 55mm has an
exact 4x5 ratio.
My 6x7 negatives measure 56mm x 69mm and my
6x4.5 negatives measure 42.5mm x 55mm. So, printing
full negative the 6x7 has 66% more negative area, not
100%. As said both have ratios very nearly 4x5. The
square format actually does a little better as a full
44mm is available. Dan
It has become my new hobby, so i'll add to this here too by pointing out that the difference between a 6x7 image and a 6x4.5 image is a factor of about 1.2 - 1.3.
So make a print from your favourite negative (doesn't matter what format or camera was used to take it), make a print of the same negative that is 1.3x larger, compare the prints, and behold the reason why you should or should not want to haul a heavy 6x7 camera around rather than a smaller and lighter 6x4.5.
If you think the difference in quality is significant, you need the 6x7. If not, pick the one that's more convenient.
I think i know what the choice will be...