I think as the tails increase, the power increases exponentially, so the gap of power is greater between the beasts as they go up.
Hmm thats a 50/50 question because Kishi might try to balance the kyubis power by using naruto as the yang side to show the bond between them not only in power but in friendship so i am not sure.Accepted..afterall naruto's d main character and kyuubi's inside him...But i need to know if kyuubi's really gonna get YANG chakra?