Aspirin vs. Ibuprofen vs. Acetaminophen

I’ve heard previously that 4 grams of acetaminophen was the maximum therapeudic dose. I was also told that 7.5 grams was considered a lethal dose. So, what I’d like to know is, what happens if you ingest 5 or 6 grams? Would it kill some people, but not others? Is there an LD50 for acetaminophen for humans?