RE: Two 5s packs or 1- 10s pack
I find more pro's to the 2 5s packs, though I run both. The two big advantages that I see to owning and running 5s packs is A) I can use them in 5s airplanes (62" Osiris for example which my son flies), and B) I've had a cell go bad and I'm only replacing one 5s pack rather than the entire 10s pack. So there's some mix and match opportunity, though I'll admit I tend to run them and maintain them as a pair.
The weight savings of the 10s pack is very small assuming your comparing apples to apples.