What about his stuff?
Miller's run of strong starts is a little longer, and his stuff is probably miles better. The reports about Millwood's stuff when he started the year on a MiLB contract for the Yankees weren't good. Given his age/injury history, I see no reason to expect that's changed.
I mean, when Lackey/Matsuzaka were busy soiling themselves at the start of the year, Brandon Duckworth was pitching well in Pawtucket, but I don't think you would have wanted him up with the Sox, because he has the stuff of a career AAA pitcher, which is what it sounds like Millwood has now. At some point, the good stuff on the resume, the stuff from years ago, gets wiped away as the talent fades. I think that needs to be taken into consideration with Millwood.