and cooling? I also assume you would get more Dust with lots of smaller 120mm fans in the case?
Of course higher total airflow is better for cooling.
But in reality it isn't that simple because fan specs are mostly exaggerated BS and the fact that lowering speed of the fan lowers maximum pressure it can generate. (meaning bigger airflow decreasing effect of impedance)
Amount of "inhaled" dust is naturally related to amount of airflow.
Noise of the fan again consists from two "components": Noises of the fan itself and turbulence noises.
Bad bearing/motor keeps some noise regardless of RPM and bad construction materials can make fan resonate creating additional ringing tones. That's why for good acoustics it's better to use strictly common standard size fans for having good range of different fans from different makers available and easy replaceability of bad/worn out fans.
Turbulence noise depends on amount of airflow and linear speed at which blades move through air. High speed fan will always keep lot of noise (like those tiny CPU heatsink fans decade ago) because of its blades moving fast and also higher airflow itself causes more noise. Also you can't just keep increasing size of fan and lowering RPM without limits because for retaining pressure generating capability you can't keep lowering speed at which blades move through the air. And replacing multiple smaller fans with one big at same RPM isn't necessarily any better acoustically because of longer blades having much higher linear speed at which they move through the air.
And big size also causes problems for positioning them. Extra airflow simply doesn't benefit components if it's going through wrong places. Smaller fans with theoretically less airflow/cooling can cool components equally well if airflow is well controlled and concentrated to right places instead of being misdirected away from components. (like top fans often do)
