The Boomer and Athena models are physically identical but otherwise subtlely different. Three recognized Boomer as the Final Cylon.
Okay, that argument is self-defeating. Three only has the faces of the Final Five to go by. If Boomer and Athena are physically the same, then Three wouldn't know the difference.
Says who? She only saw the faces of Athena (on New Caprica) and Boomer on the hub, yet she immediatelly recognized either, and no it's not because of hair styling. Cylons can pick out individuals within models, without fail. It is no stretch at all that D'Anna could do the same in a vision, since we don't even know how the Cylons can identify themselves with such accuracy, despite them being seemingly identical.
There is now info on the 5th: http://spoilergeeks.blogspot.com/200...ica-scoop.html
from Mark Stern, a Sci Fi Channel exec.: the final Cylon reveal will be "organic and satisfying" and not "some day player from season one."
Thanks for the Galactica sitrep blog, for pointing this out.
So, the final Cylon will not be a glorified extra, it will be someone who is or was an integral part of the show.