Wow, just caught up to this, weird.... Do I dare wade in? Okay, I agree with Xpress on the cell count issue. Theory and practicality are a little different. Of course 12S will have more rocket ship power than 6S. It think there were some Andrew Jesky videos a few months back where he was testing his 73 Laser on 12S and it was insane power compared to his videos running 8S, it was rather dramatic, I couldn't help but think I could not tame that kind of power.
[MENTION=3728]Bushwacker[/MENTION], regarding your twin 6S 4000 packs, seems like that will be rather heavy for his size airframe (especially being 65C). I would think you'd want to be in the 2700 to 3300 6S battery range.