Most 5/8 meters have flow performances similar to 3/4 meters. You can't put a large meter on a small line. They don't fit. If your property is too large to water with 10 gpm, then bite the bullet and have a new service installed. Depending on your town (go ahead and tell us), the new service ($$$) may have a payback, since a separate meter won't get included in the sewerage charge.