questions - How to answer this "as ... as" comparison?

With the question, "Is [noun1] as [adjective] as [noun2]?", should one answer in the negative or affirmative when [noun1] is more [adjective] than [noun2]?

Example:

Animal      Top speed  
=======     =========  
gazelle     40mph  
deer        40mph  
lion        50mph 

Easy cases:

Q: Is a gazelle as fast as a lion?
A: No, it isn't.

Q: Is a gazelle as fast as a deer?
A: Yes, it is.

But should the following be answered in the affirmative or negative:

Q: Is a lion as fast as a gazelle?

Some possible answers:

A: Yes, (in fact) it is faster. [My preference]
A: No, it is faster.

My foreign wife is teaching a children's English class as I write this, and she just asked me to explain how to answer this last "as...as" question. Unfortunately, the textbook she's using avoids the above issue. And my wife is skeptical of my preferred answer (above); hence, my appeal to the experts here.