Steve, I think you already made a decision, but I prefer it on 6s. 6s at 2500HS this heli flys amazingly. its light even with a 5000ma 6s pack in it. even the spyder packs feel light in this heli.
with that being said, I do not like sharing packs with my 700 though. I know a lot of guys do that, but to me, seems like you age the packs at different rates like that. I prefer to have my 700 packs, and then my 550 packs but that is just me...