The 6 A, PMU8318 products efficiency curves show the various efficiency levels at various Voltage levels and also at various switching frequency levels. This product family peaks at 95% efficiency at full load at 5.5 V_OUT and at 1.35 MHz switching frequency. On the opposite side of the spectrum at 1 V_OUT at 350 kHz it is hitting 88% efficiency at full load. There are also other graphs here showing the efficiency levels at various input levels for comparison.