Actually, I do think they rate the 5700 for 3S or 12cells. It's just under 65k at 3S and just over 65k with 12cells. Keeping in mind that the Mamba Max motors are rated unloaded, it should be fine...but it's gonna get hot easier.
Here's a link to a recent thread about a guy using a 5700 on 12cells in a rusty and getting into the mid 60's:
http://www.rc-monster.com/forum/show...6643#post96643