I am assuming that the OP is looking for something like those resolution tests one sees for 35mm lenses (in the past) and DSLR lenses currently - e.g. lpmm numbers for centre and corners at various apertures (and focal lengths for zooms).

I've never seen any comprehensive test for the Mamiya 645 system. They may be out there though. The one I remember seeing was for a particular lens, and it was in the context of comparing the lens when used on an adapter for a smaller frame digital camera, with lenses designed specifically for that camera.

In my experience, unless the photography is limited to flat subjects, the determination of what is needed in the way of depth of field is way more important than the relative differences in resolving power that various apertures may give.