I think it is more to do with the fact that the course through the southern ocean they have following seas, so pushing the boat to do a couple of thousand miles on the plane* is safer that dropping of the back of a wave and to be hit by the following wave.
ETA: Planing is when the boat is going faster than its own bow wave, which lifts the bow out of the water and reduces drag, giving a much high speed than the theoretical maximum hull speed.