I am using EmergencyResCapacity( 1.5ft^3 ) for all engines and stock. This speeds up the brake release time by a good margin.
I also have these two in my eng files, AirBrakesMainResVolume( 14.5 ) which means there is not a lot to recharge and this ORTSMainResChargingRate ( 2.074 ) for the rate of charge.