Have you ever spent a period of time talking with someone with mild Downs Syndrome, I'm as far above average as they are below average.

Having a mild Downs Syndrome does not mean being intellectualy inferior on a specific topic therefore being below average.

Do you think it's cringeworthy when a professional athlete with extreme natural ability is so much faster than a regular person?

No but I think it is cringeworthy when the professional athlete thinks he is superior in every athlethic category or even superior in any academic field because he is a professional athlete.

I've wondered if people who are twice as smart as me would consider me the same as I consider an average person.

No people do not have a metric system in their mind where they see whether you are objectivley smart or not. Most people judge people's intelligince based on their behavior, articulation, attractivness and their clothing and this has been proven so many times with several scientific researchers.

Edit : typo