Also with running two individual master cylinders and no booster, the internal bore of the master cylinder is smaller than compared to a boosted system so that there is a higher hydraulic gain.
Put really simply, smaller master cylinder bore and larger slave cylinder bore equals more gain. However adequate fluid displacement needs to be taken into account too.
Twin reservoir dual circuit master cylinders are designed if one circuit (front or rear) fails then you still have braking on the remaining circuit.