I guess the only drawback I see with the XLS vs. the LS is its collapsed height. It is over 28" long collapsed, where as the LS is a little over 22" long. If I wanted to travel with the tripod, a 22" one would fit in a carry-on, where as a 28" one would not. At the moment that is the last thing I guess I need to decide on.
Neither would do well as a carryon, and either would fit in a checked suitcase. That's actually why I have two tripods - the TQC-14 with BH-30 ballhead in its quiver bag fits inside my Storm im2500 carryon hard case, and is quite suitable for anything up to and including a white zoom (70-200/2.8, 100-400, 28-300). It would hold the 600 II, but if I were to travel with that, the TVC-33 would go in checked luggage.