Cooling performance wise, the Heaetkiller 3.0 is the second best water block I ever tested. Due to new tubing for my test equipment, flowrate cannot be compared to old tests, but temperature seems to be within 0.2C with the little higher flowrate, I retested 2 blocks and the measures temps were within 0.2C, but other blocks might behave differently with a change in flowrate, so don't blame me for the results posted below.

Temperature delta:

HK 3.0:
38.8 C (Eheim 1046)
37.2 C (Laing DDC-1T)

EK Supreme:
42.8 C (Eheim 1046)
42.7 C (Laing DDC-1T)

Testing mythology:

Asus Maximus Formula, QX6700 @ 3.46 GHz, 1.5 V, 30 minutes Prime 95, 3-5 mounts depending on variation, listed values are the difference of the average water and the average CPU temperature.