Mathana,
In addition to what Rene said, I would also like to point out the importance of having DMVPN running in Phase 3. As you probably know, one of the most important advantages of Phase 3 is that the Hub is used in the control plane, but hardly at all in the data plane (unless the traffic destination is behind the hub). Once you implement “ip nhrp redirect” on the Hub and “ip nhrp shortcut” on the Spokes, almost all spoke-to-spoke traffic will completely bypass the Hub.
Being in Phase 3 should go a long way in combating the problem you talk about where high spoke bandwidth could overwhelm the Hub.
--Andrew