will 3s a123 at 9.9v and 2300 mah get close to 15 minutes? or would I need 4s? or even 2s2p 6.6v and 4600 which I can charge up without having to get a new charger?

I guess I need to really decide on batteries before buying a new medusa motor. Wouldn't I want a higher kv if I was going to use only 6.6v? What is the target rpm? 30,000 rpm? And what size pinion for speeds of around 40mph max on 2.2 tires?