1. GSP would become dust against a man of Poundstone's size, strength and athleticism
2. Mariusz HAS lost a tonne of size (and strength, obviously)
3. Mariusz is a far inferior fighter than all those he has fought ... and he still does reasonably well (holds his own, as it were). This should tell you something.
4. All this "gassed" bullshit needs to stop. True, cardio plays a HUGE role in sport fighting (and to a much lesser extent, real fighting), but to imagine that a pro strongman is unable to "go" for a period of time is foolhardy.
Hope all this helps.