Ah, now that opens up a very wide area of discussion!
It would all depend on the ditance flown and the coresponding fuel load.
As far as payload alone goes, a full load of passengers in such a widebody, together with their luggage, would come to something in the region of 45 tons. The maximum payload of a B747-400 is in the region of 125 tons.
But if the leg is a long a high fuel load would be required thus restricting your payload available. Plus, of course, bearing in mind that you would be using the bellies alone for the freight (except combi aircraft), structural limitations would apply.
As you can see, not a simple question to answer as there are too many variables involved.
Wish I could help you more without rewriting complete manuals!
