According to recorded weather history a class 5 hurricane is the
biggest so the media says.  How big is the biggest hurricane according
to geology and anthropology?  Specifically has the gulf of mexico seen
a migration in maya culture because of a major hurricane preserved in
the anthropologic and rock record that was pre recorded weather
history and how big have these pre historical hurricanes been??
Perhaps what we would call a class twenty hurricane?  Does the
Smithsonian institute in Tuxtla and Papantla headed by Dr. Jeffrey
Wilkerson profess there was a lost mayan city that was evacuated
because of a massive hurricane?

check this out for an explaination of the scale
http://www.nhc.noaa.gov/aboutsshs.shtml

As you can see the scale is as follows:

74-95 mph          cat 1
96-110 mph         cat 2
111-130 mph        cat 3
131-155 mph        cat 4
155- or greater MPH Cat 5

So by definition there is no such thing as a cat 20 since everything
above 156 mph is cat 5.

That being said this scale averages about 20 mph per catagory, if we
extrapolate that out to a cat 20, the wind speed woudl be in the range
of 450-500 mph. to get that kind of speed you have to start talking
about other planets. See:

http://www.space.com/scienceastronomy/solarsystem/solar_system_weather_010306-1.html

Finally here is a NOAA site that talks about the highest winds in a
tropical cycolne

http://www.aoml.noaa.gov/hrd/tcfaq/E1.html

Hope that helps.