Hi SortieIII
You are quite right, the Classic and -400 are quite different, but the comparison made was just for simplicity, as I worked both the Classic and 340 on the same route - was never lucky enough to fly the -400!
The -400 is faster, but also burns more than the 340-600, and, comparing the Fuel Flight Plans for the 2 aircraft from HKG to JNB, the -340 seems to carry more payload than the -400 as well. Of course, the gas use by the 340 is also about 25 tons less, so this cost is reduced.
Cheers