Hasselblad A12V / A16

Would 30mm shots look good with an A12v (vertical 4.5x6) or an A16 back (6x4.5)?

Are the Hasselblad film notches present in A12V negatives, or is it exactly the same as cropping from 6x6?

I like having the borders, seeing exactly what I'm going to get through the viewfinder, and not cropping negatives.

Would the fisheye effect be present in all of the corners or just the two corners that aren't affected by the back's mask?

Might be nice to switch up the format depending on the location, and not always have square skateboard shots and portraits from the Hasselblad.

Thoughts?

How about getting a screen with horizontal and vertical crop lines for 6x4.5? Or cut a mask from a light neutral density gel and lay in the hood? I know this doesn't give you a black border, but this can be done with a piece of cardboard laid on the easel after exposure.

If the purity of not cropping is important, then I guess seems to me the A16 with 16 shots makes more sense than throwing away all that film space. A 90 degree prism will make verticals possible.

I own the 42170 screen (acute matte with grid lines and microprism). I didn't realize the outer grid lines outlined the 6x4.5 format until I scoured the Internet for answers last night. Also realized the A12V is pretty much pointless unless I really want the film notches to be on the long side of the negative, but then it sacrifices 4 shots per 120 roll compared to the A16 back. I ended up buying a BGN A16 back from KEH, and am going to re-seal it when it arrives (have extra foam seals). I don't own or want a 90 degree prism, so for the occasional vertical shots I'll just deal with using my PM-5 (it doesn't seem that much of a pain holding it vertical, and can always tripod mount it)

Is there such thing as a rotatable prism finder (pm5, or sideways angle finder type deal) so if the camera is held for vertical shots i can look down instead of from the side? If not, does Kiev make something like that?