How Fast Do You Speak?

In her graduate Spanish methodology course that she's taking online this semester, my wife wrote the following on one assignment:

En cuanto a la pronunciación no tengo ningún problema porque me crié en México, pero si debo tener cuidado con mi fluidez y no ir a mil por hora y así dejar a mis estudiantes preguntándose lo que yo dije o mencioné.

Translation: In regard to pronunciation, I don't have any problem because I grew up in Mexico, but I do need to be careful with my speed so I don't leave my students behind wondering what I said.

Her teacher liked the comment and said that it even made him laugh (not quite sure why, unless it reminded him of some classroom situations). What is always interesting to me is that language learners invariably make the statement, "[Insert whatever language] speakers talk SO fast." And yet, the truth is, we all speak fast in languages we know well. Though I will grant that some languages tend to be spoken a bit faster than others, generally I think [ALERT: unproven assertion] it is more the person speaking (personality, speech tendencies, social situation) than the language being spoken that determines speed.