I have concerns about Peavy as well, but when he's good he can be a very good pitcher. My problem is that it feels like we're covering a band aid with a band aid, i.e. covering an injured player with another injury prone player. It can go very bad very fast. Fortunately Workman has shown that he can really pitch, at least so far, so he's a good #6/7 man.
If the Sox acquire a SP, who the heck do we move when Buchholz comes back? My best guess would be a 6 man rotation or Dempster goes to the pen? He's thrown there before, and you're certainly not going to put Lester, Buch, Peavy, Lackey, or Doubront in the pen. 6 man rotation to save bullets for the PS, but do you want to limit the starts that Buch, Lackey, Doubront, and Peavy gives you?