It's possible for it to outsell the ps3, but even that's unlikely, imo. Last year the 360 had a price drop in NA and Halo 3 going into the holiday season, yet the ps3 managed to eek out a victory.
Last year's sales, for reference:
http://vgchartz.com/hwtable.php?cons[]=PS3&cons[]=X360®[]=Total&start=39362&end=39453