Hello, the 450d is optional optimized for airflow and comes with 2 140mm intake fans and one 120mm exhaust fan, but the mastercase 5 has 2 140mm fans for intake and another 140mm exhaust fan and because the mc 5 is modular you can move the hdd bays to maximise airflow even more. So for airflow vet the mastercase 5.
(But both are great choices)