if you don't need the pi to stack I've found the Argon One to be a good case for both overclocked 4's and 5's. The fan is somewhat weedy and the airflow is ques

if you don't need the pi to stack I've found the Argon One to be a good case for both overclocked 4's and 5's. The fan is somewhat weedy and the airflow is questionable, but the entire case acts as a heatsink. As far as thermal mass goes I don't know of any that beat it. And additionally, you get a Pi case that puts all the ports on one edge where they belong instead of forcing you to make cable squids on your workbench/desk.