I ran a game with 8 people. We were all in high school and had various work schedules, so it eventually devolved into two games a week with a different mix of 4-5 people.
When we actually had all 8, it was unwieldy at first. If your players can form some kind of hierarchy in terms of decision-making, it really streamlines things.
Combat was the hardest part because I had to throw a lot at them and it was hectic.