15-20 items might be me, when typing text before I make a typo ;)
I have seen real writers who type 200+/min without stopping and any errors/backspace, that is what I was thinking of. Them doing paragraph breaks might help here.
Which BTW points out another TODO with the current system (you might be aware, just to make sure): word boundaries are not checked for, so if one writes a lot of sentences in a row, and then does an Undo step, all sentences are gone.