The cars just work better with 5 or 6S. I have been running 6S for almost 2 years (I have a 5S car as well). The biggest problem with 6S is the shape of the currently sold packs. I will always recomend 6S to everyone but beware when shopping for a pack to look at the measurments closely to make sure they will fit in your tray (& under your body). I'm currently running Hyperion G3 6S in 2600 & 2200mAh size packs but had to customize my trays to get them in (2mm to wide or way too tall if you put them in on there side) for my Mugen with either RCM or Losi battery trays. The best fitting pack for my car was the Thunder power 6S 2650 (older 25C pack).