I recognize that there's violent agreement among the posters thus far that McQuaid wouldn't move Miler to the bench. I agree with that and would go a little further. Before the playoffs started and ignoring Miller's flu, I would have ranked Miller as the Bs' third best defensemen overall (behind Chara and Boychuck). In his own zone, he's not that far behind Boychuck. The man just does almost everything right there. Now Dougie and Krug both played quite well thus far, and of course both do more offensively, but Miller is so solid defensively that he's simply essential in my view. He seems to win every one on one battle and just erases offensive players with consistency. He reminds me of Soderberg in the offensive zone.
My point is that Miller has come so far that he's not even in the conversation regarding McQuaid. Seids for Bart is a move you have to make if Seidenberg is ready to go. The latter seems highly unlikely, as noted by all, but what a high class problem that would be. I might consider McQuaid for Bart, too. I don't feel as strong either way on that one. Bart's propensity for brain farts can't be fully ignored; mistakes in the playoffs can be very unforgiving.
