I've used 6.0v flight packs for many years without any problems. The total flight time is slightly decreased, but the servo strength is increased by about 20%. The pack weighs 20% more. You have no fear of damage using the equipment you describe. Most of our electronics (digital not included) are designed to handle 4.8 - 6.0v packs.

Given the problems and special equipment needed for other types of batteries, I'd stick with Ni-Cads. They're easy to properly maintain and charge and very forgiving of errors in both.

For increased flight times, increase the mAh, not the voltage, of both the TX and RX packs. An "overnight" (14-16 hours) charger output for a Ni-Cad battery is C/10. That is, the battery pack capacity in mAh divided by 10. A 600 mAh pack will require a charger that puts out at least 60 mAh.

For me, 6.0 is the way to go!

Dr.1