He's at his best weight and should remain till he finds it difficult to make weight, which isn't the case right now and not even close.
He may weigh 160 when not training but he doesn't have the power of a true middle weight . Moving up in weight would be a bad move on cotto part , He would only face bigger stronger fighter with even more resilience to his punching power ..
I can't belive how much people have discredited Cotto since the Margarito fight. IMO, he still beat's all 140-154 champ's out there. (Not named Antonio Margarito) I await their rematch. And Cotto's return.