Im not running the 540 arms, so as Sam said, 10" is the biggest i can go. And its all i need.
Sam, you have the FM4008 motors, which is what i have had on mine since new.
They worked ok, but the bearings are shot and the grub screws holding the bell to the motor shafts, have stripped so many times its not funny any more.
I will use them for a basher quad at some time to just throw around and beat the crap out of. Or i may replace the bearings and sell them.
Ordered my batteries from Hobby King yesterday, and they are already shipped