Welcome to APUG.

I notice that you are a "pinhole" shooter. That tells me that you might be working with very low light levels (at the film plane) and correspondingly long exposure times. If that is the case, most likely you will be dealing with reciprocity failure as well.

As different films experience reciprocity failure in different ways, you may want to clarify that your question applies to long exposures (if it does) so those who use the film in those conditions can help you.

If you are working under more typical circumstances (e.g. f/8 @ 1/250 sec), the film won't experience reciprocity failure, so the different aperture and shutter speed combinations that are reciprocals of each other will give you the same results.

Technically speaking, the ISO of the film is a set amount, determined under specific conditions. Those conditions are very different from the conditions encountered in pinhole work, so it is usually necessary to determine different Exposure Indices (EIs) for metering under those conditions.

And of course, many people will prefer to use an EI that is different than the ISO of the film when metering under "normal" conditions, because they prefer how the film responds when they meter that way. The post above from rjbuzzclick is an example of that.