Hmmmm.............10 week old Lipos. But you posted noticing some slight puffing after only having them 4 weeks?
http://www.rc-monster.com/forum/showthread.php?t=21373
I would say they've been on their way down for awhile now.
If your fan wasn't kicking in, IMO, you couldn't have been pushing the amp draw that hard.
My MMM fan cycles quite often really on 4S.