But I don't think Maersk (or anyone) does much work shipping across land on Antarctica. They do supply some of the research stations[1], but these tend to be on the coast.
Given that, I'd imagine somewhere in the middle on Antarctica would be about the furthest.
This immediately makes me want to calculate the Maersk pole of inaccessibility just to prove them wrong. Maybe xkcd can get on it. (see http://en.wikipedia.org/wiki/Pole_of_inaccessibility)