Impedence is a very important, but often ignored point. It determines just how much of a load your pack will accept without browning out. And yes, running parallel packs cuts impedence in half. IE - Two 10 mOhm packs in parallel equals 5 mOhms.
FYI -
http://www.hangtimes.com/index.html is one of the few battery vendors that list impedence. The lower the better.
> Jim