Arguing with investors will hardly ever change their mind. Investors have one or both of the following characteristics: 1) they know what they are talking about, 2) they are convinced that they know what they are talking about. A successful investor probably has a lot of 1).
Repeating the same argument over and over does not get you anywhere. Pulling out an unexpected, little-know fact though, might get you some points, and showing that your are not a dogmatic person to work with, but can listen and work constructively with a Board member gets you lots of points.