My understanding of the key difference between the 330 and the 340 is the maximum take-off weight and you can see the extra landing gear on 340 models due to this. MTOW being higher on the 340 allows it to carry more fuel even with a full cargo load which is the critical factor in the extended range. The 330 could achieve the same range if fully loaded with fuel but it couldn't do it with full cargo.
I didn't consider the additional fuel, which the 340 is capable of carrying upon take-off.
Makes a lot of sense and thanks for the insight.
Reminds me of another dirty, little aviation secret:
An airline may bump you, despite the fact that the plane has empty seats. The reason, again, is take-off weight.
It's a lot more profitable to load an additional container than you. Even considering costs like compensation, hotel rooms and even a rebooking to a different airline.
The source for that is my sister, who worked ground handling for the (now defunct) Swissair.
