He's looked more comfortable since moving up in weight. His stamina for his last few fights at 130, although good, didn't look too impressive IMO, which is why I think he struggled in those figths and would starch JMM at 135 and above.
Plus Pacs fighting above his natural weight so he has to put in more of an effort. Pac clearly has outstanding stamina not the very best tho.
Calzaghe has nothing behind his punches, everyone knows it's far more draining to throw harder punches. Pacquiao has the best stamina IMO.