The current A340 model cruises at 0.82.
The new 500/600 series with the Trent Engines should cruise at 0.83-0.84 and hopefully climb a bit better. (Airbus figures).
The new 380 is supposed to do 0.86 or greater,Airbus figures again.
The A320 manages 0.78 econ cruise and will do 0.8 with increased fuel burn.(only recommended in smooth air!).
Dont know where the 0.76 comes from.Apart from being high altitude turbulence penetration speed in the 320.
The A340 sells because it burns around 6-7 tons per hour as compared with 12-13 tons per hour for a 747 classic and 10-11 tons (I think)per hour for the 747-400.It also has an enourmous cargo capacity.This along with mixed fleet flying endear them to accountants even if some pilots seem to hate the sight of them.