what will mannys weight gain affect most?

his bank account

from the way he conducts his workouts and sparring, definitely not stamina. spped? we'll see but if there's any decrease it would be very unnoticable. his power WILL go up.

speed? stamina? power? speed and stamina

Most likely stamina, the weight gain is not big enough to affect his speed. His power might likely stay the same or maybe even increase, it's just Oscar is not a smallish lightweight, so the effect of Manny's punch might be lessened. I agree. Fighting someone so much bigger than any other opponent will wear him down. Like Edwin Valero said, he'll be wearing his tongue like a necktie in the later rounds.

His movement round the ring, plus being in with a rangy welterweight like Oscar may make him look short armed in comparision!

ide say stamina his body isnt used to working in a enviorment like that with the extra weight on him, maybe even his speed with be slowed a bit. who knows WAR PAC MAN

All..he'll get tired quicker as well.