The "super slide" format was the format one obtained when shooting slide film in 127 cameras. The slides - 46mm x 46mm typically - fit in mounts that will work in 35mm slide projectors.
@OP: about projector: life is too short - if you can buy it - go for it. We all spend money on extra equipment that we don't really need, but if it will make you happy - GO! :)
What about using one of those overhead transparency projectors that used to be so common in classrooms?
Even second hand 6X7 projectors cost an arm and a leg, http://www.ffordes.com/product/12032311582981 that's why I never bought a 6X7 camera, I have a Rollei 6X6 projector for my Mamiya TLR slides.
I wonder if it's possible to build your own 6x7cm projector. I have access to a 3D printer...