Just to add to that Ryan, the 2cm^2 piston will require twice as much fluid to move as the 1cm^1, you're just using the fluids as levers. Within reason all is good but go to the extremes of large and a huge multi piston caliper mounted to a stock master will feel mushy since your pedal will have to move so much further to move enough fluid to build the pressure it takes to stop the car (mind you it would still probably stop the car way faster than stock ;)).