I hate to go down this Code.
As your feeders are not carrying the entire load of the residence, you cannot use '05-'08 310.15(B)(6) {'11 310.15(B)(7) }
As best I recall prior to the '08 Code, as long as your calculated load on each panel was less than 180 amps, you could use 4/0 SER with a 200 amp OCP device.
Starting in '08, many folks would not accept that installation unless you OCP device was 150 amps based on 338.10
In '11, the 150 amp protection would be required IF the SER was installed in insulation. If not in insulation, the 180 amp rating is o.k.
That said, enforcement of this varies considerably.