A '69 wing originally built for an aircraft 20% lighter than todays 400 (don't fly 'em so only guessing).
Add more wing span (at a later date), then throw on some winglets, (at a later date).
Maybe there has not been huge advancements in aerodynamics since 69, but I would be very surprised if the A380 wing, designed from scatch, could not beat the 400 (plus any future wing span increases) for aerodynamic efficency.