Do you want the wider aperture for reducing depth of field or for low light?

If it's for depth of field, medium format has less than 35mm anyway so you should be o.k.

If If it's for low light then I don't know. Judging by questions like these and questions about super high ISOs on other forums, weddings must be much darker now than they were when my father used to photograph them with fairly normal lenses and ISO 160 film!