Martin: at the end probably simplest is to treat fans as some kind of black box with specific airflow/pressure/noise characteristics. Too many variables are at play there that can enhance or destroy performance/noise ratio. Good silent bearing & engine can allow fan to run faster with acceptable noise allowing in return to compensate sub par design of blades, good blade design can push more air with more pressure at lower rpm-s allowing to mask inefficiencies on engine part or thin fan thickness. And inconsistent manufacturing quality can destroy whatever potential both design of blades and engine might have.