True, the brakes can't provide more braking than the conditions allow, though even in that case if its critical one might waste braking distance using autobrakes because the reverers might provide a lot more braking than the deceleration 'lost' due to the antiskid on the brakes. (which will reduce the brake pressure again if the deceleration rate is above MAX rate if in any other mode than RTO)
Ah, A300-FO, I didn't realize you were talking about RTO, well in that case the 733 applies maximum brake pressure when the throttles are retarded to idle above 90 knots and the autobrakes will be disarmed when the speed brake lever is moved to the down position during the rejected takeoff. Interesting to find out how it works on the 300!
