Let's check past sales :
1st xbox360 price cut (THAT WAS MORE IMPORTANT BVIOUSLY !!!)
http://vgchartz.com/hwcomps.php?cons1=®1=Total+Other&cons2=PS3®2=Total+Other&cons3=X360®3=Total+Other&start=39509&end=39614
first week : little bump : 50k=>64k
second week : big bump : 64k=>95k
others weeks : 95k=>91k=>80k=>74k=>71k (then GTA4)
For the second price cut (right now)
first week : little bump : 46k=>59k
second week big bump : 59k=>97k
others weeks : 94k=>77k already !!! => ? => ? => ?
Time to Work !