8 people for dinner on Sat. - Gonzo, Otto or ???
I'm a Gonzo fan and I've been there with a group of 8. We were quite comfortable at a large round table. The only problem was that each member of the party was rather far from the people across the table. Since Gonzo is a rather noisy room, it was hard to hear each other.
A party of 8 is great, though, for splitting a variety of Gonzo's grilled pizzas.
I recently had a dinner with a large group at Crispo. They have a semi private room, it may be called the Majestic. It may be too late to reserve it but it is worth the effort. I love Gonzo and Otto as well but I am not sure how they would accomodate such a large group, especially Gonzo which is pretty tight. Da Andrea has a few large round tables and Bianca, although small, has at least 1 table that could accomodate a larger group. There are larger well know places that I am not mentioning only because you said "hidden gems".