I am sorry, but i think they should make the deal. It has been too long since the Sox won a Series and they should do what they can to get another solid arm. Here is my reasoning:
McCarthy is a prospect. The Sox have a lot of young arms at the Lower A levels, including their first round pick this year - Lance Broadway (some say he will be ready sooner than later for the Bigs). While McCarthy has shown some signs of potential greatness, who knows if he puts it all together? Everyone thought Jeremy Reed and Olivo were going to be the next young stars on the South Side. While both are still young, they would not be starters on this year's team. Olivo has actually been on the decline while Reed has only shown he is an average/capable major league player. (.254 avg, 2Hr's - little power, and only 2sb's). What I am saying is, while McCarthy might be a great MLB pitcher someday, there's an equal chance he might not.
Marte was getting shelled at the beginning of the year and control was a major issue. He went on the DL and has been lights out since. I would hate to give him up but if that's what needs to happen, so be it.
Burnett is 28, and yeah, had major arm surgery but has come back from it and still throw gas. While Freddy G. and Contreras can get the ball up to around 95, they aren't pure fireballers like Burnett is. He would be a great change of pace in a rotation with more finesse pitchers like Buerhle and Garland. AJ is just entering into his prime and if they can sign him to a longer term deal it would be great.
As for Contreras and El Duque, they scare the h#ll out of me with their incosistency. Either or both would be solid contributors in middle relief. So while not directly acquiring a reliever, trading for Burnett would add to the pen.
I do agree they will need another LRP though. Wagner or Guardado would be great but unrealistic. I am not sure what they would need to give up for one of those guys, probably a lot.
Finally, another rumor around here is that Reinsdorf has given Williams the green light to spend as much as necessary. He probably sees that this will be his best chance to actually win a Series and attendance has been up. If they have to mortgage some of the future, so be it. Bring a World Series title to the South Side! I am sick of waiting for next year...let the Cubs keep that slogan.