A glider champion told me that Nmihs were a bad idea, because they have a significantly larger voltage drop when placed under load when compeard to Nicads. The problem with this is that when you do a snap roll or lower the flaps, the current drain from the high performance servos put a large load on the battery........ the voltage supply goes down so much that the reciever goes into failsafe or it goes out of range- hence broken model.
I do not know wether this problem occurs at 6 volts though.
Maybe it doesn't, but im sticking with good old nicads.
Luke