That unit from the article sounds very temperature sensitive. I'd be wary of throwing a precision unit like that out of spec and out of calibration.
FWIW I've noctua-swapped so many things including an oscilloscope.
The last rubidium oscillator I played with, had to heat the vapor cell within the physics package, but then prevent that from overheating the rest of the unit, so it specified mounting to a heatsink. There was no heatsink recommendation given, just a certain package temperature as reported by sensor value X in the diagnostic data page. Get below that and you're golden. Get too much below that and you're wasting extra energy in the heater. Which is harmless, it just drives power consumption up.
So depending on how the unit's thermals work out, a slightly less aggressive fan may end up being mildly beneficial.
One of my slightly embarassing ones was the fan on one of my Nanlite lights was always on, do I thought to swap it with a noctua one so at least it'll probably be quieter.
When I took it apart, it turns out it was already a 12cm noctua... Black edition.
You can also get non-Noctua hydrodynamic bearing fans with polycarbonate blades and silicone mounts which are supposed to be very quiet, but I've never compared one against a Noctua. Anyone done a comparison?
In the case of this Rb oscillator, it is temperature sensitive, but also built for pretty extreme environments.
I'm not too worried about this particular application, because the clock will be in an air conditioned environment, and I'm monitoring the clock accuracy to +/- 2ns from another GPSDO / rubidium clock. The performance before and after the fan swap is within my measurement noise for 24H, though I haven't done 30+ day measurements and ADEV comparison. Still working on a consistent test setup.
Considering the new airflow rating is 9.4 m^3/h (vs 16.8[2]), yes it sounds like plenty of headroom.
[0] https://safran-navigation-timing.com/wp-content/uploads/2023...
[1] https://cdn-adepci5.actonsoftware.com/acton/cdna/28343/f-bf4...
Not with Noctua and the likes, not always at least. These fans are quiet, but they are not made of magic fairy dust. They simply max out at lower flow rates than some of the the noisy, high-RPM fans people replace with them. Those 40 mm Noctuas, apart from voltage options, don't really come in many varieties.
It's a trade-off - you definitely lose the upper end of the device's original temperature range, but if it's stable under your conditions - great. How do you find out? Well, you replace the fans and check if it sizzles or not.
And funnily enough, a LOT of equipment these days isn't made with formal thermal design, they simply throw in high-cfm fans and... check if it sizzles. It usually doesn't because there's plenty of headroom. It's loud, but who cares since it's not meant to sit on your bench.
Source: replaced PSU and chassis fans in countless pieces of network and test & measurement equipment.