Denny - maybe my recollection was 3.5v was the safe level for Spekky stuff. I had a lock-out with my A9/Optima 7 Hitec stuff that cost me a $1k plane. I was foolish and used the ICE 75 BEC on 4 digital servos.
I should have used a 2s LiFe pack and I would still be flying that plane. I had the ICE BEC set at 6v output and alarm at 5.8v and it would kick off periodically and I didn't do anything! A .2v drop sure indicates the BEC is not keeping up. Not sure where the reboot voltage was but I was on final approach and the plane just kept flying right into our trees at the end of the runway.
I had plenty of warnings including guys going don't trust the ICE BEC but I didn't listen to them or my system when it kicked off the alarm. Pretty stupid eh?
Lesson learned. LiFe or separate BEC for all 4s planes and up for me now. My new large 6s Telemaster Plus actually has one 2s 640 mAh pack for just the SPC and a Castle 10amp BEC for the 6 analog servos. I will likely replace the BEC with a 2100 LiFe pack soon.