It'd be almost impossible for FFXIII on the X360 to outsell the PS3 version, without a Japanese release. That's like 2 big, burly boxers fighting, and one boxer has his hands tied behind his back.
Japan WILL see no less than 1m units sold on the PS3, but i think it could hit 1.4-1.8m based on the preformance of MGS4.
North America will go the X360's way due to the trending of the X360's install base. I think XIII in NA could see anywhere from a 250,000-1,000,000 unit difference between the X360 and PS3.
Europe will probably go the PS3's way, but not by a large margin: 250,000-500,000 units should be expected.
So in the West, the X360 should lead by upto 500,000 units. Problem is, Japan adds in 1 million+ units, and suddenly the PS3 version will sell more. Again, you can't think very reasonably that a game can launch in 2 of 3 regions and do better when said title preforms equally in all 3 regions.
Back from the dead, I'm afraid.
