[marzac2]

I would say 5S if your planning on racing it. 6S would be way fast for a track.

And why 6S hardcase? Do you have to use hardcase? It will make your battery hotter than if it were soft cased. By about 10-20 degrees. If you can do so, I would forget about the hardcase and choose the JUST AS SAFE OR SAFER alternative. Hardcases are for sanctioning bodies like ROAR to use as a disguise for safer batteries. Not necessarily safer by any means. And you will save a lot of money with the soft case too.