I think the biggest key to the series is Rondo. We pretty much know what we're gonna get everywhere else.
If Rondo is Rondo, the Celtics win in 5.
If Rondo plays conservative/slow, then Celtics in 7.
edit: But to make an official prediction - what better time for Rondo to be Rondo than in Madison Square Garden when the Knicks have weak basket protection? Rondo will be Rondo, and the C's will win in 5.