Sorry for being late to this discussion, but I am one of the few - in Norway anyway - who has used the Bronica PG 50mm
at the same time as the Pentax 67 45mm over several years. Therefore I have some basis for comparison.
(I've used the P67 55-100 zoom instead of the P67 55mm, but that's for another story...) Bronica and Pentax
are both very good. Neither the Bronica PG50mm nor the P67 45mm are at their best fully open, but stop it down
to F:8 and both are crystal clear and pin sharp across the entire image surface. The Bronica has slightly more
vignetting, but has better distortion and chromatic aberration than the P67 45mm. I believe that both of these lenses
are among the weakest in their representative brands. This does not mean that they should be excluded, but used according
to their limitations. Proper wide angle on proper medium format gives fantastic results. They attract attention and are
the pictures that have earned me the most money.