My dual monitor setup is a lot more productive since I turned one monitor on its head (color coded for your reference):
I’ve got the right-hand (extra) monitor in landscape mode for working with documents, and do most of my actual work on the laptop monitor (on the left).
It’s arguable if dual monitors (or one single large monitor) is more productive. But I can definitely tell you that this setup, where one monitor is very obviously the “reference document” monitor seems to get the benefits of both.