That sizing guide is somewhat old--Perspective hadn't existed long when it was published--and doesn't provide satisfactory advice for Perspective users, IMNSHO. It really is only good for Vision applications. See this for more robust advice:
Also, note that the sizing guides do not include database operations, but a system dedicated to just an Ignition gateway. (In production, databases should always be on separate systems, and sized for the quantity of data to be stored.)
Edit: I just went back to see that the sizing guide has been updated for Cloud Edition, but still recommends client connections only suitable for Vision. It really needs to distinguish Vision clients from Perspective clients. Perspective clients put way more load on a gateway than Vision clients.