Aside Kim, Most of the members think that Porcello is a #3, although he had a #4/5 role with the Tigers.
Just for the record. I wouldn't be against Porcello if he were supposed to fill a #3 role at the right price. IMO the Sox have bet a lot hoping that this guy could climb 1 or 2 steps upstairs while taxing him some pressure to a guy who has never been in that role. Sure, they have their reasons (young, defense, etc), but in the end his profile suggests me that he will always depend from the guys behind him, reason why I think he will stay at best on what his track record suggests.
Anyways, as I said in the offseason, I would have used Panda, Porcello (wouldn't make him an extension like that) and HR money to assemble a rotation like this:
Lester
Shields
Porcello
Masterson
Buch, and/or whoever else you want.
Betts
Pedroia
Papi
Napoli
Vic
XB
Castillo
WM
Vasquez
Sure the offense doesn't look as good as it is right now, but rounding them with some good utility players and prospects like Holt, Nava, etc could have been good enough to score above AVG.
Anyways, let's see if FOs's strategy works out.