Good luck - it looks to be very tasty. I assume you have already met your goal in the Sweet Stout (16) category? That would seem the most appropriate category here with Oreo cereal, if you were adding a bit of lactose (which you are not)....or perhaps SHV 30A due to the chocolate as a spice? The 16 B works, though, since you have oats added, of course, just wondering about the judges reaction to it in this category.
Good luck and let us know how it goes. A small batch of it would be nice to have around for a change of pace on the stout front. I am due to brew something stout-ish and this might just be my inspiration to get it done.