With my old Pentax MX I can go up to 1/1000 which I trust it is fast enough for almost any situation, but 1/500 or 1/400 is a whole different case.
Yes, there are various ways of overcoming this limitation on a brightly lit situation like stopping down or using a filter etc. but this might compromise image quality which voids the whole point of having a MF camera IMO.
That "whole different case" is only one stop.
Perhaps a slower film? Put PanF in the camera and you'll have 1/400 at f5.6 in bright sun.