"... The fastest airplane out there today is the 747. Not one of them has been able to match the cruise speed of the 747. That indicates to me that it’s a high-technology airplane ..." Joe Sutter [0]

wing sweep alone doesn't explain why the 747 is the fastest subsonic transport to date. If it did, competitors would have copied the idea. I'm curious why? Boeing describe it as a combination of wing design, engine, electro-mechanical systems. Maybe I should ask Boeing.

[0] http://www.boeingblogs.com/randy/archives/2006/08/father_kno...

Because the penalty for that speed is higher fuel burn. That's why Boeing is having trouble selling the 747-8, and why four-engine airliners in general are getting phased out.

My source for the wing sweep thing is also Joe Sutter, in his wonderful book. Also highly recommend Widebody, by Clive Irving, which is sadly out of print.