If you use 5cell packs, even on a 40% aircraft, you're not going to see voltages low enough to hit the receiver clipping point. If you do, you've got other more serious problems. And my using 5cell dual packs in a redundant configuration, you lower the risk even more. You would need an abnormally high load to get dual 5cell packs in good condition to drop anywhere near 3volts.
Futaba is the only PCM receiver I know of that has a battery failsafe feature. If the voltage drops below its set point, the throttle goes to idle regardless of the stick position. You then bring the throttle stick to idle, then back up to power and it resets itself, and you can continue to fly in order land safely.
From what I understand on clipping with receivers is that if the voltage drops below the receivers threshold, the receiver stops working, but does not go into failsafe. Since it stops working, it removes all the load from the servos which removes the load that started the low voltage in the first place. The voltage rises, and the receiver starts working again. It all happens extremely fast, and if the pilot noticed, it would feel much like a sluggish response and not like a failsafe event. Think in terms of something like ABS brakes, where it pulsates on and off rapidly, but doesn't cease to function properly. Even with clipping, the pilot has control of the airplane.
Here are a bunch of recent threads on setting up 40% sized airplanes, PCM and PPM, wiring, etc.
http://www.rcuniverse.com/showthread...hreadid=465411
http://www.rcuniverse.com/showthread...hreadid=436492
http://www.rcuniverse.com/showthread...hreadid=424119
http://www.rcuniverse.com/showthread...hreadid=424119
http://www.rcuniverse.com/showthread...hreadid=289142
http://www.rcuniverse.com/showthread...hreadid=130469
http://www.rcuniverse.com/showthread...hreadid=130687
http://www.rcuniverse.com/showthread...hreadid=473062
http://www.rcuniverse.com/showthread...hreadid=355152
http://www.rcuniverse.com/showthread...hreadid=339931
http://www.rcuniverse.com/showthread...hreadid=246442
http://www.rcuniverse.com/showthread...hreadid=401764]