I've found for outback riding the biggest heaviest bike I would take would be a KLR, or maybe a F650, both heavier than I like if I'm doing more than pretty tame dirt roads.
A good lighter bike from a 250 to 400 would do fine as well, though might be challenged to run 70 on the highway, small price to pay if you plan to do a lot of rough offroad to make that easier.
Better to use a bike that weighs in at closer to 300lb like a Honda WR, XL, DR650, KTM LC4 or so with a 5 gallon tank, and pack light. For me if I'm over 30lbs of gear I'm too heavy.
Makes for a much more pleasant ride that way, and lets you go pretty much anywhere. Not to mention picking up heavier bikes after a wipeout (which is more likely with a heavier or overpacked bike) can be a real bear when your wiped out too, or hurt.
I like to pack using a lot of the same practices an ultra lightweight backpacker does.
I also will never own a dual sport with hard side cases for luggage, I've seen too many very nasty leg breaks from folks stabbing a foot down in a rough spot and having the case hit the back of their legs, and guys going down and getting nasty breaks. Maybe soft side bags like "dirt bagz" brand but hard side cases and dirt riding do not mix that well IMO.
