I have heard that some people have problem with drift in the tx/rx so the setting of the switch between atti/gps was drifting and causing strange behavior.
If you set the second level at 3.3V per cell without line loss, it means that with line loss 0.1V it will be 3.2V flying...
So it is not bad for the lipo to go lower than 3.3V under load?
I too have the voltage check on. First the bec shows a red flash for a while and then it starts to descend... Have you mounted your bec so its visible during flight?
I have a naza F450 dji kit with graupner 10x5 and a gopro2 flying with a 3s 4200mah, that gives me about 15-17min in atti mode.
Basic gains are P150, R150, Y120, V150 and atti are P110, R110.
What kind of flight times are you aiming for?
What would give the best flight time?
3s 4000mah and 10x5 or 4s 4000mah and 8x5, the 3s is 300g and the 4s is 400g.
Why should you not use 4s and 10" props?