Before we begin, a word or two about the test setup. We'll use our trust Core i7 4790K Quad-core processor. Current age six-core processors and even some 8-core AMD ones still have close to the same TDP / thermal performance, as this processor. In fact, the AMD ones even have a lower thermal signature.
We're purely looking at the basics here. I've used an old (2011) Noctua NH-C14 CPU cooler here, the performance is good but not perfect. This way any differences in temperatures versus airflow can be detected a notch better. Modern Noctua coolers perform better, ergo the result set would be closer to each other in temperatures. We'll tweak the ~90W TDP processor towards 4600 MHz on all cores (fixed). We fire off 1.3 Volts at the processor. With AIDA we select the CPU stress test to maintain an even as possible highly stressed workload on the processor. And then we test the fans at 4V and 12V to see what kind of effect the fans have on cooling performance. The results are pretty surprising, as the different fans all have quite an extensive effect on performance.
As I mentioned, I consider the 4V baseline test the most representable as to what you guys have configured in your PC. Ergo the result set above is the most representable, IMHO. Leading at the top of the charts, it's no surprise, of course, the fans with the best airflow.
You can see that Noctua is yielding results with their 4 years of development for their Sterrox - steroids? :-) enhanced products. The NF-A12x25 PWM and FLEX lead the performance at 64 Degrees C. The NF-A12x25 ULN perform worse, but that has a low RPM configuration and thus offers less airflow, so that makes perfect sense. The NF-P14 is an old fan, however a 140mm one, it's running 4 degrees C higher over the FLX. The F12 PWM is a more recent fan released by Noctua, that one as well performs worse. I mean it's all trivial stuff for sure. But again of 3 to 4 degrees with just a better fan, is rather impressive to see.
When moving to a way too aggressive 12V (your fans at 100%), the results close in on each other as the airflow obviously increases. The two NF-A12 FLX and PWM, however, keep the lead with a healthy margin.