I agree with your premise, but I disagree with the following...
I know Francona has been too loyal to veterans at times, but I hope he gives Lester the Opening day start, followed by Buccholz and then Beckett. There are 2 reasons for this, the first reason is because that's where they belong. The second reason is that putting Beckett 3rd in the rotation will hopefully light a fire under his ass and motivate him to a great season.
Over the course of a season, I think who the "#1" is is pretty irrelevant anyway.
Sabathia has an edge over any of our guys because he eats innings like he eats everything else. I think it's pretty close otherwise between Sabathia and Lester – so if we're talking about a postseason rotation, I wouldn't be afraid to bet on Lester.
I don't think that Burnett is the Yankees' second best starter anymore (if he ever was)...and Beckett seems pretty capable of being anywhere from #1 to #7 on the Sox. He could be the best. Or he could just give up 80 HR and be a worse option than Wakefield or Doubront. But if we go with the two ex-Marlins, I'd say Beckett ≥ Burnett.
Any of the expected starters vs. Andy Pettitte: Pettitte has generally been more durable than it seems (to me). Last year was one of only 6 seasons in his 96 year career below 200 IP, and one of only 4 below 190 IP. He's also the same age as my grandmother, though, so I'm inclined to think that any Red Sox starter, including 5 inning Matsuzaka, is probably going to end up pitching more innings than Pettitte. If Pettitte continues last year's HGH regimen, then he could well be "better" than Lackey, Matsuzaka, or Bad Beckett (please, God, not Bad Beckett) – but innings are important. And Andy isn't going to pitch a lot of them.
Hughes, whatever, he's pretty good. He'll probably get better. Ivannova (I think that's a brand of cat food), or other mystery starter TBD, is an unknown. Lackey is going to have an ERA of 4 point something, and Matsuzaka is going to probably make Francona bust out those wigs from those NESN commercials last year, just so he can pull all the hair out. Edge, gyroball.