I carried out an ad hoc bit of experimentation on a few very experienced, advanced lifters in my gym. One of them knew what RPE was and considered it useful, though he didn't actually use it.
On the second set of the working set, I asked them to rate their RPE. They all estimated 7 or 8 which means they had 2-3 reps left in the tank. After a short rest I asked them to see how many reps they could actually achieve. The results were surprising, but in hindsight perhaps they weren't surprising at all.
How many additional reps do you think they did ?