do you have tractor requirement specs for the disc? cat 1 or2? I'd say there are 2 biggies for a 7040, the implement weight and HP requirement. remember, 3 pt. specs on a tractor are from 24" out, the disc will project a lot more. assume you're considering 4wd.
sorry can't really specifically answer your question, but do know the 85/9540 HD 12 sp. trans. is rated @ 7k+ on the 3 pt. whereas the 7040 is i think slightly under 3k. if you're considering an implement that big you may look @ the 85/95 model to grow with future needs in the field.
there's a section in the owners manual of each model that gives limits for various implements: plow, b'hog, disc, etc. am sure your dealer would let you review when looking @ a given model.