There's actually supposed to be a way to use 600 film in an original SX-70, too -- not only is it faster, but it's a couple bucks cheaper per pack as well. The pack and image dimesions, and camera specs are identical; the conversion of the older cameras, as I recall, requires opening up the front panel (around the lens and photocell) and replacing a resistor to reduce exposure by two stops. I keep thinking about this; I have an SX-70, and I've never been very happy with the images it produces, but faster film would give both smaller lens opening and faster shutter, which couldn't hurt. But with the price of film, it's hard to justify in comparison to my 6x9 folders, unless for subject matter one doesn't want a processor to see (and for some reason don't want to shoot on digital).