Early A dual reservoir conversion

Hi, I did a master cylinder upgrade to a dual master, but I feel like I don't have enough pressure to stop the car quickly if I had to. The brakes were bled, and it seems to have a high enough pedal, but when I try to apply brakes I feel like there isn't enough stopping power. I also upgraded to a 8 3/4" rear end with 10" brakes recently. could it be that the piston is not large enough for the system? I'm thinking of doing a disc brake swap to help, but if there is not enough pressure for drums, will there be enough for discs?