I 've fished with the three lines you are talking about, braking strenght or breaking point is only measuring the tensile pull at which the line breaks, it 's not counting other factors like manageability, user friendlyness, abrassion resitance, plasticity, memory and such.
XT is indeed more resistant than Big Game and a lot more resitant than XL in an area, abrassion resitance, so there are many factors involved and not just the line diameter when it comes to selecting the line type that best suits your needs.
For me from the three, the best "all round" in all aspects in 10-12 lb test class is Big Game, if I need tougher line I go with XT, XL is a great line where abrassion resitance is not as important but where or when limpness is more important.