I don't believe range hood specifications. They are fake numbers.
Do you have a leaf blower? A powerful leaf blower with 400 CFM spec blowers a lot of air and makes a lot of noise. Can a kitchen hood with 600 CFM to 900 CFM make not much noise?
Range hoods to keep the motor noise down mostly use induction motors which run inherently at low speed, and the path to exhaust the air restrict the diameter of the duct.
The length of the duct and any bends in the exhaust duct created air turbulent back pressure, and filters can restrict air flow.
I would be surprised in actual use, a typical hood can exhaust more than 200 CFM.
dcarch