My thoughts concerning the OP:
the current gap is 6.7 million consoles, and there is about 7 weeks left till the end of 2009. My prediction is that the minimum gap will be 5.5 million (which means the ps3 will have to outsell the 360 by 170k weekly average) and a maximum gap of 6.2 million (which means the ps3 will outsell the 360 by 70k weekly average). Here are the factors that i think will play a role:
1) the holiday boost in sales will most likely be heaviest in the US and UK, the 360's best regions
2) holiday shoppers looking for gifts will more likely choose cheaper gift options, i think the 360 arcade unit sales will take off
3)Final Fantasy 13 doesnt launch in Japan until the last 2 weeks of the year (if im not mistaken), so a prolonged spike in ps3 sales will not be accounted for in 2009
4) Microsoft is competitive and will not allow their lead to be squandered so easily, i wouldnt be suprised if we saw alot of holiday incentives like that recently offered by walmart or just better bundles (ex: forza 3 and mw2 in europe)
It will really come down to how holiday boost pans out