I'd say choose a 400 ISO film
I use a variety of ISO 400 C-41 B&W and color films, and set the meter to 250.
Primarily with the slower lenses of medium-format rigs and interior shots, it'll be ISO 800 film with meter set to 500.
Why set meter lower than box speed? Better/richer shadow detail and color density, smoother grain, and to give a margin for error to avoid the dreaded underexposure! 🙂