Craps, the thing as I understand it about a123s is that the mah on them can be decieving. From what I have read, it appears that you get better longevity of runtime than what the mah would lead you to believe. why exactly, I don't really know.
A123 has packs out from what I have seen in pictures that fit excellent in 1/10 scale vehicles. no shaving of the sides needed (saw it in a pic for the review of the IFS TA05). If they put two of them together ( I think they are 2200mah?) to get the 4400mah, could give you the excellent runtime, not have as much high COG, and give a better weight for the vehicle. Plus, the fast charge thing and elimination of fire concerns is a big bonus too.
The voltage thing is an issue, but, since its mod, just go with a hotter motor. spec classes will be an issue however.
I love my lipos, but can't argue that if A123 can get better fitting packs out there, they could be the way to go.