OK, but table B.310.1 is part of Annex B, and therefore not part of the requirements of the NEC.
Table 310.16 is the one to use. 3/0 cu in the 75 degree column is rated for 200amp, so 3/0 it is.
I seem to remember that the rule of thumb for reducing the neutral conductor is two sizes smaller, which would result in a 1/0 cu conductor. Take extra time in calculating this, as there are a number of rules to follow to do this.
As triple has mentioned, the use of the table 310.15(B)(6) would result in a smaller conductor, but it has some believers that it can not be used for a subpanel. Since you are installing a 400amp service, where will the other part of the load be going? If it will be for outbuildings, then perhaps the smaller wire will be justifiable, since the subpanel will indeed be the "main power feeder" to the residence.
Hope my, and the other's, information has helped.
Rick
