It' very hard to say.
Consider one extreme- the anniversary party this past summer during which our friends opened the '82 Latour, among many other trophies- there were 30 people in attendance, and everyone that wanted a taste got one- in fact a few of us got a couple of tastes. In fact, only a few of those wines were finished that first night. Yes, tastes were very small, but i don't think anyone cared much about the size of the pour- it was about celebrating a special night with friends and some terrific wines. So if a crowd is of one mind and respectful of one another, a trophy can indeed be enjoyed by a lot of people.
I would never open a trophy bottle just for Domino and I, unless it was an anniversary bottle...though even then I don't know if I could do it. I'd have to have already shared a bottle or have more bottles in the cellar to share another time- then I could burn one on just the two of us. Still, I think we'd probably invite a few friends to celebrate with us and share the experience.
So in my world, I think 5-8 is about right, perhaps three couples being ideal. Everyone can still get a fairly good-sized pour that could be followed over a couple of hours if need be.