The version that fought Corrales or Floyd the first time (let's say he fought at 140, not having to lose the extra water would only help him) probably knocks out Cotto, who was fragile at 140.
That's kind of unfair though don't you think? Given that scenario i agree Castillo gets a late hard earned stoppage. An "honest" 140 (if there's such a thing) I think Cotto gets a razor close decision. Regardless of who wins both guys would be in serious pain for days after.
If you mean that Cotto has to drain and Castillo has to drain less, maybe.. but Cotto carries the accompanying size advantage. It would be a great fight either way..
Cotto at his weakest...and Castillo at what could be his best...because he doesn't have to kill or cheat himself making 135..... Anyway Castillo by late TKO 11-12 ....or Cotto by close disputable decision...