For a while I toyed with the thought of getting a 6x17cm or maybe 6x24cm but had to realise that owning a 8x10" with a Nikkor 120SW I wouldn't need one.
Cropping is the way to go as others have said before me.
If you want, you can make some cardboard cutouts in the sizes you want and use them to check the image as cropped. I find this helpful to see if the height inside the cropped image makes sense or not.