CAN you use 4.8V and get away with.... yep.

When 6V Lithium is available to you is 4.8V even a comparable option.. NO WAY...

6V regulated lithium or even better Lithium A123 setups give you faster servos with better response and power. PLUS you are so much lighter than NiCad milliamp for milliamp. 5Cell (6V) NiMH packs are a viable option, but they do weigh a good bit more than Lithium. The only bad thing there is to Lithium is that if a cell fails you are pretty much dead meat,, where with NiMH if a cell fails you will get a tell tale reduced performance but at least you will have something to land with. Lithium has proven itself to be very reliable, but after about 1 year of 6 flights a week, I typically start watching them really closely and usually will just replace them. And 2600mah is not overkill in a < 1.00 plane. It is a LOT of battery capacity, but for the tradeoff of the alternative in NiCad or NiMH and not that much difference in cost a 2600mah Lithium pack in a Mojo60 will save you a couple of ounces and give you way more capacity.. THere is no better option than Lithium Ion, Polymer or even Lithium A123 batteries,,,, which by the way totally A123 totally blows all the other options away. A123 has sick burst discharge capacity, requires no regulators and is totally stable unlike the other lithium options. PLUS you can charge A123 packs in about 1l4-1/5th the time it takes to charge a LiPo or Li-Ion of equal capacity.