Emmett Gowin made an interesting body of work in the 1960s using a 90mm lens on 8x10. Suffice it to say that they are undistorted circular images that don't cover the whole frame- and are quite beautiful.
It seems to me that the larger the film format, the less need there is for lenses of extreme focal length. The longest I have used with 8x10 is a 19"/480mm lens and that was pretty long. I'd start with a 300 or 360mm lens; those are considered 'normal' for the format, and using one for a while will tell you which (if any) other lenses you might want.
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