you can sorta get more line pressure, just have to push the pedsal further, as the smaller bore master cant go as far as the big one, you get more pressure
but you would have locked the brakes up by then

if your still using single piston calipers all round i doubt that you would need a bigger master, im running 4 piston front and drum rear(until the diff is done) and a 7/8th master, the pedal is like a rock....has about an inch or 2 travel, if you push really hard
but the car is pretty well on its way to being stationary by then