Why wouldn't this fight be at 126? That's where Gamboa's been fighting and where JuanMA is destined to go sooner or later.
My instincts tells me that it won't happen until a bit down the road, since fighters generally like to wait until a fight develops into a big money fight, which will probably be by the time they are both at 130 lbs.
Gamboa wins via ko in 8, his speed will be too much and he has power as well. He won't stand there and slug it out with Lopez- he will dance around and tag him with precise counter punches.