Predicted temp difference between CPU and ambient, the lower the better:
Yes, it would seem the DDC can outperform the D4 in a restrictive circuit as it dumps less heat, which makes up for the slightly lower flow rate.
In a less restrictive loop, the amount of heat 'saved' may not be enough to overcome the gains due to increased flow with the D4.
ATM, I think the decision is more likely to be influenced by your noise tolerance levels
