More like four.
Look at 2008 vs 2009 similar months.
I suppose it could still be considered a boost if numbers don't rise, but are prevented from going lower?
According to your own charts, seems about 6 months - and almost 10, if you count the ~17,000 difference in March/April of 2009 (even though PS3 outsold the 360 in this period - it relinquished it two months later,showing a sustained boost for 360 sales).
Don't know about you - but I think you just proved yourself wrong.