<font face="Verdana, Arial, Helvetica, sans-serif" size="2">The important thing is as soon as you reach bmi gold put the remainder of your miles for that year into MP </font>
Exactly my tactic.
One thing to bear in mind. Although *A Gold is meant to offer seamless benefits, in practice both airlines treat their own Golds better depending on which card is in the PNR. If I'm travelling MAN-ORD/IAD I have been treated like royalty by BD, the only exception being when I had my MP number in the PNR. United doesn't treat anyone like royalty, but the worst journeys have all been when I'm earning on the BD card.