The mini does 6.74 Gflops/W. At the default clock rate of 1200 MHz the Pi 3 can achieve 6.2 Gflops. However, without a heatsink the CPU will instantly throttle

The mini does 6.74 Gflops/W. At the default clock rate of 1200 MHz the Pi 3 can achieve 6.2 Gflops. However, without a heatsink the CPU will instantly throttle to half speed and average about 3.1 Gflops. So the mini is 3 to 6 times as efficient.