I'm usually at 4 + garlic fingers, or sometimes 6 if nothing else and really hungry, so I voted 5. 8+ had been known as "normal" in my youth. And higher. We won't talk about "all-you-can-eat" night at Pizza Hut a long time ago... (many bad choices there, including going to Pizza Hut at all)
And then there's my minimum record: 1.25. Of course this was in Chicago, at a little place my brother's co-workers told him about that I think was called "Tony's Pizza Peddlers" out near-ish to Schaumberg (long time ago (2000), I didn't live there, so don't hold me to name or location accuracy, and I've searched recently and think it's closed now). Ever since going there, I know what actual deep-dish pizza is. I call it "Lasagna-Pizza" because it's SO damned deep. 1.25 pieces eaten. I had a piece, and split another piece with my brother, and we each ate half of what we'd divided it, and thus 1.25. And I was FULL. And this was in the time of 8+ being normal, and shortly after my brother and I consuming a pan of lasagna between us in one sitting. And this pizza did us in. SOOOOO full.