Also got to think about max zero fuel weight.
I have flown a max'ed out zfw 747-400 from Perth to Singapore (4.5 hours) before with only a half load of passengers due to the cargo weight.
About 60 tonnes of payload I guess, of which only 20 tonnes down to pax. I believe something to do with the Australian coin minting coins for Singapore or some such....
Would have looked good for staff travel, 350+ capacity, 170+ free seats, sorry sir, it's weight limited!