Kit Guru test methodology give no details of how the testing is done. Is air temp into cooler / raidiator monitored and recorded same time as CPU temp is recorded? Are fan speeds the same for all cooler when temps are recordced? Is noise leve the same on all cooers when temps are recorded? Therfore Kit Guru testing is ambiguous and invalid. The same lack of testing methodology applies to tom'sHardware reveiw. Lots of fancy graphs without any explaination of test procedure makes them invalid, even though it's only CLCs being tested.
Even with this dubious testing at maximum OC, CLC temps range from 57.1-66.5c with D15 being 63.1c .. 3.4c better than H100 and 6c warmer than Castle 240DX. and DRP4 is 69.1c, only2.6c warmer than warmest CLC. Noise levels have DRP4 at 39.4dB, quieter than quietest CLC at 41.2dB, D15 at 44.1dB and H100 at 53.7dB. Human ear needs about 3dB change in sound pressure to register a difference in sound level, and 10dB change sounds half / twice as loud to human ear. So to our ears D15 sounds the same as quietest CLC and loudest CLC sounds almost twice as loud as D15. Compound all of this with D15 being one of if not the most expensive air cooler on the market while coolers like TRUE Spirit 140 Power cool as well as D15 at same fan speed costs about 4/7th's as much. CLCs range from £50 to £232.99 while air coolers range from about £9 to NH-D15 chromax.black £92.99, Cooler Master Wraith Ripper at £119.99 and most expensive Prolimatech Genisus w/ Silent Wings 3 PWM High Speed fans. That leaves approximately another 63 CLC's costing more than most expensive air cooler listed on OcUK.
That is your assumption. One not backed up with any unbiased testing of air coolers to verify your claim.
We need air cooler testing done with system noise level and air temp going into cooler and radiator recorded at same time CPU temp is ran on your system for us to have data that will either verify or refute your claim.