Maximum - 13 million
Minimum - 6 million
Reasoning:
On the side favoring the X360, it will achieve a maximum of 10-11 million before mid/late March when Sony *may* drop the price of the Playstation 3. Should Sony wait until later in the year, then the gap is sure to grow to 12-13 million before a price cut is initiated. The gap could theoretically go higher if Sony's price cut was not very good (a $50 cut), or Microsoft countered with something better (such as a Slim model that sold very well).
On the side favoring the PS3, Sony could make aggressive cuts early, pitting the X360 and PS3 in a daily dogfight in March, for a 10m gap, which dwindles as the year goes on. I'd say 5m is the *bare minimum*, but given the various possibilities, 6m would be a 'very good' scenario.
Back from the dead, I'm afraid.
