There is very subtle difference in a few charger specs that do not tell the entire story. Using the same 24v supply charging 6s the Powerlab will hit its INPUT current limit (40 amps) before its output current limit. With the same configuration the 306b will hit is OUTPUT (30 amps) current limit before hitting its input current limit.
Why is this important? Its because the output wattage is relative to the pack voltage. For the iCharger to hit its limit of 756 watts, the pack needs to be nearly full. It will start the charge around 700 watts and slowly ramp up.
The Powerlab6 starts it's charge at 860 watts (160 more than the 306b) and sustains that output through the entire CC (constant current) stage. This means the Powerlab6 is putting in more mah earlier in the charge. This will fill the pack faster than the 306b's slow rampup. The result is a much faster CC stage. See below:
This test was intended to show the differences in the high output stage of charging where the maximum output of the charger is the only factor being tested. To show the entire charge cycle to the end can be impacted and influenced by charger settings and pack condition. In addition, higher charge rates have inherently longer CV stages due to the nature of the chemistry and its voltage sag characteristics. The test is to demonstrate the raw power capabilities during the entire high current stage of the charge cycle. This is the reason that one cannot use a single specification to accurately compare two chargers.
More on this test here