I think you should just show your key. We were there Memorial Day weekend and we had the concierge in lounge at the HRH make a reservation at Mythos, and when we got there we still were made to wait 20 minutes. After the first 10 minutes I asked why we had not been seated; and the hostess said they seated in order of arrival . . . I could hardly believe my ears; I asked her why why did they even take reservations if they didn't honor them and she just repeated herself that they seated people in order of arrival.
So maybe make the reservation . . . . but be prepared to wait anyway.