Mascherano is a full time CB. That's all he plays for Barca, he won a Champions League final there. Pique doesn't have competition? Silva would give him that. Puyol is injury prone, but there's no guarantee that will continue. With the addition of Silva and more rotation, that would protect him from injuries. Adriano is emergency back up, he has some experience there now. He's not been great there, but he's done ok. If we can draw with Madrid with him being CB, that's more than good enough for fifth choice.