You can maneuver indefinitely while blacked out at at least 3.5-5 Gs. Only your vision is affected at this point. Your motor control, speech and hearing are not impared.
That is based on my personal experience.
GLOC (gravity-induced loss of conciousness) occures at about 9+ Gs after a few seconds, but WWII planes never reached 9Gs in one piece.
miko