well ff13 has sold almost 2 millions in japan on ps3
it may perform well on xbox due to low price (2,900 yen) and right period of releasing christmas time HOLIDAYS time
if it sells more than 300 units, it will push system about 20k so around 20-22k in that week i believe
in general holidays for xbox in japan this year may be the best ever but that 's not guarranted