Hi - I think it also depends on the Length - if you get L30 i say get 29x30 in 805A. I regret not getting it and got 28x30 and its tight.. i still manage to fit it but you will notice the wasit sits a bit lower than how Shioner's suppose to fit. Thus if you bend forward your plumber's butt clevage will be showing.
I also have Shioner 817H 29x30, so I understand its a bit looser than average. But 805A is stiff & thick so I still recommend go w/ 29.