Thanks Fornax! I tried to reproduce your numbers, but then I realised I can just look at the product sheet. It says that at ~60Pa the airflow drops to 50m3/h. That's pretty straightforward. Could I say that if I put two in parallel the pressure drop halves to 30Pa, giving me 2*130m3/h = 260m3/h or does it not work like that?
Now with the power of datasheets, the Can Fan one looks much more attractive. The RK 125LS has a flow of ~180m3/h when Pa = ~60 on its lowest setting. I see I could pick one up for just 70 euro's in my own city. And it operates at 43W at that setting, so that's significantly lower than 60W.
Unfortunately it doesn't list any sound measurements, though with a 30% better power efficiency I'd be surprised if it made more noise.
Looking forward to your more detailed response