And I'm currently running it on low, otoh, with a more silent fan, I expect that the CPU fan will start to annoy me instead
On low, is the Antec CFM and noise level acceptable to you? If so, why fix something that isn't broke.
If not, consider the Scythe S flex as an upgrade - likely getting a bit more CFM with a bit less noise.
Well no, I want to get the noise level down. Not sure how much good comparing manufacturer specs actually is though
I mean, the Noctua is speced 800-1800 RPM, 15.3-31.2 CFM and 7-17 dBA depending on which voltage adapter you run it on. If I'd run it on medium speed (using the L.N.A adapter) it'd be specced at 23 CFM @ 10 dBA, and I'm not sure how "true" these numbers are