My numbers aren’t made up, though 
German mechanical engineers math with its thermodynamics rule #1 said, let me recite a not to be named masters student: “The amount of heat energy through the heatbreak is 3.1xxxJ to 4.8xxxJ for the 1.75 V6 version at a 250degC heaterblock and 20degC heatsink, ignoring all other realworld factors, depending on what type of stainless steel they used”. And it is nearly double of Jouls for the 3mm heatbreak.
@Rene_Jurack The math isn’t hard. E3D specifies 303 SS so we know the conductivity. From my calculations, you only get up to ~5w for the 1.75mm version with realistic PLA printing conditions if you look only at the throat dimensions and ignore the thermal resistance of the threaded connections plus considerable thickness of 303 stainless between the throat and the M6 hot threads + M7 cold threads.
Rene can u suggest any of the water cooling parts needed such as reservoir, fan etc…