> about my ability to speak for 10 minutes about something without notes.

I'm not sure how common this sentiment is, but I would feel extraordinarily uncomfortable -to the point of feeling a bit like a fraud - if I were to speak about something continuously for 10 minutes (at a high degree of entropy, rather than just taking glancing stabs at the same observation from multiple angles) _unless_ I could do it without notes. If I could not do so I don't think I would even attempt to participate in a conversation on that subject, feeling as though I had nothing useful to contribute to the conversation.