That's what Dead Rising 2 co-producer Shin Ohara reckons, anyway.
Speaking with Gamasutra, the Japan-based developer says "Last year at Captivate we did a demo. We had a strip — It was probably like 10 metres wide and 200 metres long. We filled it with about 7,000 zombies. After about 3,000, you can't really tell the difference because it fills up the screen anyway. Over 3,000, it ruins the experience. It's not a game anymore."
He maintains that Dead Rising 2's engine could do 7000 zombies on-screen if they wanted, but yeah, that's when it becomes a tech demo, and not a game. Shame. I'm sure there's at least one instance where they could cram 7000 in and just... set them all on fire or something.