I'll give you 3-to-1 odds that Buccholz does not move to the pen, big league or otherwise, this season.
Why? Because the Red Sox see him as a potential future ace of the squad and they don't want to mess up the next 3-5+ years of their staff for bullpen help today. People with lower ceilings, like Masterson, they are more willing to put in as needed. Buchholz will be starting in Boston or Pawtucket or be injured... I don't see any other option.
Why would the Red Sox start Colon over Buchholz?
A) They can send Buchholz down to the minors without any real waves; Colon would basically demand to be traded.
B) It would allow them to more tightly regulate Clay's innings.
C) Colon wasn't that bad: 3-to-1 K-to-BB ratio and a respectable ERA for the AL East.
Now, based upon Colon's progress (or lack thereof) from injury, that might be a while, August say. But if Colon is 100% healthy and effective, it wouldn't shock me to see him start over Buchholz.
0-3 to 4-3. Worst choke in the history of baseball. Enough said.