At idle, all we really care about is noise. Sure, there's some differentiation in terms of temperature, but a well-designed cooler will reduce noise to the minimum possible level while still operating at a safe temperature.
And what we see here is that all these coolers fall into a very narrow band, with just a few outliers. The Scythe Fuma is quite a bit cooler at around the same noise level, the SilverStone AR03 is even cooler, but with a high noise level (and pretty scratchy bearings, we should add), and the Noctua NH-L12S is literally silent. At 20dB, this cooler operated at the noise floor of our test lab. The PC might as well have been shut off. There was no noise. Helping it in this regard was the fact that its fan faced the glass side panel, as opposed to the exhaust vents, and was hidden behind a metal heatsink, that likely absorbed some of its noise output. But there's no doubt that Noctua has hit a home run with its new, ultra-slim Noctua NF-A12x15 FLX, designed specifically for this cooler, but also available at retail for $20. It's amazing. Getting zero bearing noise out of a slim bearing like this one no doubt took a serious bit of engineering work.
By the way, we should note that the fan RPM readings we collected for the Arctic Freezer appear to be incorrect. The fans were clearly not running at 918RPM based on observing them, and later on, you'll see the fans reporting out at RPMs well above their maximum specification. We believe the PWM splitter included with the cooler may be distorting the readings, although we can't say if it's exactly twice as fast as actual or something in between.
Moving onto CPU-z's built-in benchmark, we find that the coolers start to diverge somewhat. Most impressive is the Scythe Fuma, with the lowest temperature and lowest noise level. Whoa. Yes, we just checked our hand-written notes to make sure this wasn't a transcription mistake. It's achieved nearly the impossible in this test. The Noctua NH-U12S and Scythe Mugen 5 stayed pretty close, but all the other coolers are just playing catch-up. A little surprising was the performance of the Cryorig H7 Quad Lumi, which was essentially on par with Noctua's slim NH-L12S. Yikes.
Turn up the heat, even on a stock eight-core Ryzen, and things spread out a bit more, but honestly, the Fuma is just way ahead. There's nothing else to say. Well, perhaps we could mention how disappointing the H7 Quad Lumi is. We checked the mount after our testing was done to make sure it had made proper contact with the CPU's heatspreader, and indeed it had. Given our previous experience with the original H7, this is a serious downgrade despite the higher price. Perhaps Ryzen's larger IHS versus the Intel CPU we tested the H7 on isn't playing to the Quad Lumi's strengths?