I see a lot of people calling this Holliday over already. That the multiplats (since the ps4 is short on exclusives?) will push the ps4 so much ahead of the x1. We haven't had 1 week of data with the xbox at 399, and it still hasn't launched in a lot of territories.
I think the x1 will build up momentum starting with the 399 Xbox. It will dwindle back down a bit but by the time it starts to get lowish the xbox will be coming out in new territories and the exclusives will start to come. Sunset overdrive, forza, dance central, then halo.
Halo MCC will sell 5+ million copies(including digital)
halo 5 will sell 10 million copies(including digital)
x1 will pass ps4 in USA, and UK.