Her is the ranking by average salary:
Kershaw
Scherzer
Lester
Verlander
Cain
Felix
Greinke
Hamels
lee
CC
Tanaka
Porcello
Price
Wainwright
Sheilds
Bailey
Lincecum
Weaver
Sanchez
And that means what? Price per WAR has skyrocketed the last few years. What you need to figure out is what the going $$/WAR was when each pitcher signed. Porcello also gets a slight boost for signing his prime years away which will always increase salaries compared to someone at age 30.
Again, the Sox are paying Porcello to be a 3.5-4 WAR pitcher on the current market. That is not ace money unles you think aces are now 3-4 WAR pitchers. I think it's an overpay but he's not getting ace money. Aces, especially those in their prime, would be getting 25+ right now. And that's only going to go up as long as salaries continue to inflate as tehy have been,