You mean like last year when they clashed? EastEnders came out top on Overnights while Downton came just ahead of it in the officials. This will happen again this year.
Last year both EastEnders and Downton started at 9:00pm
Your making it sound like they have never clashed before and that this is the first xmas Downton has gone head to head with EastEnders.
BIB - That's a mighty statement
But I fear it is said out of blind faith rather than reasoned judgement.
Last years Xmas DA came on the back of (what was seen by some) a weak 2nd series.
The Xmas ep this year follows on from a strong 3rd series.
EE is not rating as well as it has done of late - though there is no doubt the Xmas day ep will gather up it's current floating viewers on the day and I don't see the offerings elsewhere as strong enough to take them away.
However - I wouldn't be as blindly confident as you appear to be Dan - I think it's far more open than you care to acknowledge