Curry stops him in 6, in a one sided fight. The thing about Cotto is, he's a good fighter, but only for this era. He wouldnt be able to hang with prime versions of DLH, Mosley, Tito, and Ike. And he DAMN SURE wouldnt hang with the Leonard, Hearns, Duran, Benitez. Curry in his prime was good enough to hang with any of those guys, and Donald was a different class of fighter than Cotto.
I don't think Cotto would ever solve Curry's piercing jab. Cotto would have to take a lot of chances to even be in the fight and he'd just get caught with too many clean shots. Curry by mid to late round tko.
Curry dominates cotto, cutting him up and eventually stopping him inside of 10. Cotto is a real warrior with great heart, but it wouldn't be enough against curry, who was technically superior in every aspect and was much faster. Also throw in the fact that curry was a defensive genious and this spells disaster for cotto.
Like I said in my above post, Cotto is only good for this era. Curry would have destroyed him. And for that matter... Starling would have destroyed Cotto also.