From my testing (DAN Case-3700X) the AXP-90 Copper with NF-A9x14 VS NH-L9a with fan duct is 3-4C cooler.
I have done many tests (88W PPT and 100W PPT, Cinebench, Blender, Prime, always the same frequencies, voltages, power draws from the wall, ambient temps etc) and always the results was 3-4...