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.
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.