We know PS4 is sold out everywhere, so it's easy to believe 4,2M as of December 28th is sold through.
But when it comes to X1...It's not the same story, it's even the opposite.
anyway, i'm sure PS4 will beat X1 January sales, there is no other possibility. PS4 may has lower stock, but soon, X1 demand will be lower than PS4 stock ( we'll see that next week).
Mark my words.
Predictions for end of 2014 HW sales:
PS4: 17m XB1: 10m WiiU: 10m Vita: 10m