I have found the seating maps for B to be extremely accurate, right to the second. In fact, when I'm at the airport I often have the seat map for my flight open so that I can monitor the likelihood of an upgrade. Even after securing my seat, I've watched the other seats on the map get plucked up one by one as the other Elites in line get their upgrades. I even see the seat they vacated in coach as it clears. It's also helped me determine when non-revs have been "given" B class seats.

Back to your situation, six open seats for a trip all the way to LAX may not hold for too long. But it's hard to tell. Assuming it's just you, I would wait until it's down to about three seats before showing my money. But that's me playing the odds. Why do you feel the six vacant seats in B aren't accurate?