As far as quality of packs goes, it depends on what you need too. If you are running a 4S setup and need a battery that can dump 100A continuously, then you need a true 20C pack at 5Ah capacity. On the other hand, if you are going with a higher voltage setup, the "quality" of the battery pack becomes less important. This was my reasoning behind going with 5S anyway.

I figured that if I was running a motor on 4S to achieve 30K rpms at a 100A constant draw, the running a motor on 5S to achieve 30K rpms should only take 80A under the same circumstances. That's what I'm figuring anyway.

On my truggy, I went from 4S with a 7XL to 5S with an 8XL and I think it runs a little better, but definitely cooler.