It is clear that for all the pumps tested that using the #4 or #5 nozzle results in improved temperatures. It also becomes apparent that, for nozzles #4 and #5, the gain from changing to the more restrictive #5 nozzle is offset by the accompanying decrease in flow rate. Since nozzle #4 and 5 perform so closely together, I would recommend the #4 for TDX users."



Link: Procooling