I've been to Shanghai several times. While we are pushing back, a UPS 747 on the next parking bay, also going to Anchorage, AK is pushing back at the same time. After the pushback the 2 jets are facing each other on the taxiway. I've asked the UPS crews how much freight they have. Their answer: About 180,000 lbs (almost exactly the same as my MD-11).

So ... the 747 uses approximately 33% more fuel to carry the same amount of freight the EXACT same distance.

I guess that says it all ... that, and as someone else said, more engines increases the chance that you'll have an engine problem preventing departure.