I own a Bronica PS 40 mm. Despite the 95 mm filter thread, the outmost lens glass element is much smaller than those 95 mm.
This is a question for those of your using this particular lens with a square, drop-in filter system. Can I happily live with the Cokin Z-Pro filters or must I move to the X-Pro line.
The same question goes for the Lee filter system - either 100 or 150 mm?

To put the problem into context for everybody:
35mm equivalents:
i) 26 mm Horizontal field of view.
ii) 17 mm Vertical Field of view.
iii) 22 mm Diagonal field of view.

Angular fields at the 55.6x55.6 mm negative.
Horizontal and Vertical true fields: 80º.
Diagonal true field: 113º
Note: neither of these match Bronica's specification of 87º angle of view for the lens.