The benefits stack, the side effects don't.
So if you are going to be loading up on higher doses of pain relief, take half acetaminophen and half ibuprofen.
"My head is pounding. Shit...did I take this at 3PM or 5PM? I know I took it and then fell asleep, but I can't remember when. It is now 9PM, can I take more or not?"
Rationalizations like “they probably put the limit way lower than the real limit so idiots don’t OD themselves, so I can safely take a bit more” become very attractive when you’re in a lot of pain.
I know people with permanent pain due to medical conditions who have been given a doctor's approval to exceed the limits printed on the packaging (after having previously been monitored). You can exceed the limit on the packaging by one or two pills.
A bit more is often not deadly, but it's very easy to take more than a bit. When I had a messed up mouth for several days, I took the maximum doses and set timers to help me regulate the dosage throughout the day, but I sure wished I could've taken more at that time.
From personal experience if i have a headache I'll take 1000 mg all at once; it either works right away or it doesnt and I stop bothering until I've had a good nights rest...
I had only very brief experiences with longer intense pain but it made my mind into pudding and desperate knot of how-to-stop-this-at-all-costs. Normal life is not possible and sanity is not granted.