There will most likely be about a month's worth of boosted sales, leading heavy in the first week of the 20GB SKU inventory sale/clearing and tapering off until stock at $299 is depleted.
Does this have anything to do with a multi-platform game that will not be shipping before 2010? Try to use common sense rather than brand fan logic.
About the only people who will be making their decision to buy a current gen console on the basis of the FFXIII mult-platform announcement are the very same demographic of consumers who buy consoles years in advance for as of yet unreleased titles. It's a very small percentage of the overall console market.
Nothing announced during the MS conference will have a protracted effect on 360 sales comparable to the PS3 40GB SKU and it's new entry price point.
Now if MS had dropped the bombshell of price reductions across their entire product line ($229 Arcade, $299 60GB, $399 120GB) that would very likely result in a permanent increase in sales although the 360 price drops throughout Europe suggest otherwise. This is taking into account that the US is the strongest market for the Xbox brand.







