The smaller the bore the less leg pressure is needed to stop the car with no power assisted brakes up scope
I found that out the hard way when a master cylinder went south at Pomona one year and I didn't know the correct size of the master cylinder bore and replaced it with one that had a 5/16 bigger bore when I had to replace it because it wouldn't stop that car worth a hoot down shock whiney

Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)