I don't really think he gassed in the floyd fight, he got tired but still came back a bit. I believe he won Rd 8 or 9 or something. Gassing is when you're basically done.
And as for your second reply about cutting weight, I'm not saying cutting weight gives you better cardio, I'm just pointing out that he'll be smaller, and the less muscle you have the better tank you'll have.
I do believe if it goes to the later rounds he'll likely be fucked like you're saying. But my point is that I believe he'll have slightly better cardio than at 170. It won't really change much though cause you're right he'll have to finish it early. He did have a second wind against diaz in the second fight and even diaz got tired.
I think his gas tank is underrated a bit.
His power may be overrated but it doesn't matter because it's his knockout ability that not overrated. Who cares about power. If u can put guys away that's all that matters.