A larger master cylinder (bore) will give you worse brakes. The pedal will be at the very top but it will take King Kong to push it down. The smaller the master cylinder bore that will still give you enough pedal will also give you brakes with the least effort.
True, and to small of a master cylinder bore won't move enough fluid and you have even worse brakes, as they don't fully apply.
While it
may be possible to go one step smaller, if there is such a thing for your vehicle, and keep the brakes in good adjustment and the fluid toped off, I would leave things as the are. If you go changing stuff you may find out the hard way that it did not work as planed. Stick with the stock components or an aftermarket kit that is engineered to work properly.
Grigg