RE: A123 li-ion packs
they are starting to market them, although I do not know much about the packs the 600 uses. The ones you build yourself are 2.3Ah per cell, and have a slight weight penalty over lipo's. The way I have seen them marketed is 3.3v lithium ion cells, and if I remember right they are lithium nano phosphate. So those are a few terms you can search for, good luck =)
overall they are alot more stable, and alot more resistant to over discharge, fires, ect. They usually charge up to something like 4C's or about 15 min charges, and have something like a 35c discharge rate.
Oh, and I'm sure that you know that you need an a123 compatible charger =)