For those experienced in MF photography. I have had a Mamiya m645 for some years and done quite a bit of portrait photography with same. I am considering stepping up to a used Bronica SQ Ai or Mamiya RB 67. I have studied both on the 'net and found that each is considered a very good to excellent camera. I realize that Bronica is no longer made by Tamron and there is the chance of repair issues in the future. However, this question is about negative size and the actual difference between 6 x 6 and 6x7. Does that centimeter make a HUGE difference in negative quality and enlargement?