However the tech boys at BHX had it bang on, and a 787 at sea level to China, and similar distances requires 9,400ft. We are at 330ft about that so add a bit more.So the extension was necessary even for for the 787 to such places.
That seems very high, like every foot of the runway! The B777s and A330s at LHR don't appear to need that much tarmac.