Not to undermine the GMT-II, it is a very strong and reliable watch and can go to hell and back without flinching an eyelid!!
While the Sub and SD are very tough watches without a doubt, the GMT-II has gone to places like the Arctic cirlce and down to the hottest hell-holes of the Sahara desert....without any problems whatsoever.
All Rolex watches are tough as nails!!! The question is....can you take what is dished out to your Rolex?