You dont know who is the #5 since DiceK is just as much of a question mark since he's coming back from a shoulder injury. There is an inherent risk that you will need to lean on a pitcher more, ie move them up in the pecking order. A #4 starter is vital. A #5 starter can be skipped 10 times a yr and is obviously less vital (see Yankees 2009). The bottom line is....
The sox have a 1-2 punch that is really hard to find, unless your root for the Mariners. Their #3 is at least a #2 in performance and is really only a mild injury question mark. Your #4 and #5 spots are question marks since one is coming off a concerning injury and the other is entering his first full yr of big league starting. The Yankees have an ace that is the best pitcher between the two sides. They have a 2-3-4 that is durable, but not of the caliber of Beckett (when he isnt hurt) and Lackey (if he isnt hurt). Notice a theme here? There is a certain relief that you can take when you know who is taking the hill. I am pretty damn sure that 1-4 will be starting regularly thoughout the yr. The #5 spot is a question mark. For the sox, you are pretty sure 1-3 will take the hill, although a bit less sure IMO when you talk about Beckett and Lackey due to their recent injury history. My question for you, is, can you count on 30+ starts from DiceK or Buchholz? The answer is, no. Just like I cannot count on 30 starts from Joba in yr 2. It certainly may happen without a hitch. But there is an inherent amount of risk involved.