Nice find. I would imagine it really doesn't make that much difference if it is two die or one. The small nozzle gives the highest velocities. The difference in nozzle location versus heat distribution isn't that much different between the different number of dies.
However, their pump never got to very high flow rates. One issue with just putting in the nozzle, shown well in your spreadsheet, is the reduction in flow rate my adding a nozzle. In there test the 3.6mm nozzle never went past .8 gal/min.
For example, using your chart, a XSPC Res Top DDC 3.2, PA120.3, and different nozzles we see that 6.3 to 5.5 reduces area 24% but adjusted for a 10% reduction in flow increases velocity only 15%, 5.5 to 4.4 area is down 36%, flow is down 25% and velocity up 15%. From 4.4 to 3.6 area is down 33%, flow is down 24%, and velocity only up 12%.
In their graph, temps would have gone from 15.42 to 15.9 to 16.35 to 16.5. If the flow was constant the decline could have been 15.01 to 15.89 to 16.48 to 16.71. The first was a range observed in most testing of 1.1 degree; the second with constant flow was 1.7 degree.
Still, how critical is 1.7 degree to any realistic overclocking?
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