There's no doubt that a fan running continuously is easier to ignore than one that stops and starts.
The bigger the fan, the more airflow it moves for a given rotational speed - I'm really impressed with the large 120mm case fans, that can run at much slower speeds for a given airflow than the traditional 80mm fans that all computers used back in the old days. If you can make them fit, then they will definitely give you more cooling for less mechanical noise than the smaller ones.
Things like rubber mounts (even just grommets) help to avoid conducting motor noise into the chassis, and keeping air speeds low to avoid turbulence will make a big difference. Anything you can do to improve airflow really helps - it might mean enlarging holes, but for safety it might be wise to put a mesh grille to keep fingers out?
I'm sure it'll be less of an issue in the winter
